Geology of Arctic Canada: Encyclopedia Arctica Volume 1: Geology and Allied Subjects

CONTENTS

GEOLOGY OF ARCTIC CANADA

Introduction

Most physical and biological phenomena change with latitude. For example, polar climates and polar flora can be defined and readily dis– tinguished from their tropical counterparts. In geology such a distinction is to be observed only in the youngest rocks. There are at present no general criteria known by which a majority of the rocks, fossils, and geo– logical structures of polar regions can be identified and distinguished from the geology of equatorial or temperate parts of the world. Although some fossils have been found only in northern latitudes, it has not yet been demonstrated that they are all peculiarly arctic in character. On the con– trary, fossil evidence suggests that the polar regions have not always been as cold as they are at present, while indications of former areas of glaciations have been found in many parts of the world no longer cold. Too little is yet known to explain these observations, but they suggest that the earth has usually had a more uniformly distributed climate than at present, and that ice ages such as the recent Pleistocene glaciation have been exceptional events.

The cause of these periodic glaciations is not known. The more important periods of glaciation, at least, have followed active mountain building, but astronomic and atmospheric influence seem also to have been a factor in

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causing and controlling them.

It has been suggested that the earth’s poles have migrated with respect to its surface or that continents have drifted on the earth’s surface and so moved with respect to the poles, but the paleontological grounds for advancing these views are not conclusive. Physicists who have examined the forces available in the earth to produce such movements are unanimous in believing that they could not have occurred in Paleozoic and more recent times to the extent postulated and required by some paleontological theories. They consider that some other explanation not involving continental movements is needed. It is quite probable, therefore, that since the time of their origin the northern countries have been arranged about the pole in the same way that they are today. Many aspects of this subject are still obscure and await investigation, but this much is certain. No general characteristics are known of the fossils and the materials of the earth by which the geology of Arctic Canada can be differentiated from that of the rest of North America. The geology of those regions will, therefore, be discussed as an arbitrarily chosen part of that of the whole continent.

Our lack of knowledge of the arctic regions makes it doubly desirable to consider the geology thus, so that we can extrapolate from extensive studies in the south to tie together isolated observations farther north.

No one is familiar with the geology of all parts. The great areas re– quiring examination and difficulties of travel have resulted in separate groups of geologists working without much intercommunication, in the Yukon Territory, in the Mackenzie River Basin, and in Labrador. The District of Keewatin and the Arctic Islands have been studied only by occasional expeditions. For the same reasons, the relationship between the geology of Greenland and

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that of adjoining parts of northern Canada is scarcely known at all, but the geology of adjoining parts of Alaska and of Yukon Territory are reasonably well correlated across the 141st meridian of west longitude which forms the political boundary but follows no natural division.

Among all these groups, working in different parts of the North American Arctic, geological interpretations have differed, and it has been possible for differences to be intensified where little has been studied and where regional descriptions depend upon scanty observations. These differences of opinion and gaps in our knowledge make summarization difficult, but the task of generalization has been simplified by the general reports upon the state of geological knowledge in several of these regions which have been prepared by leading authorities and issued during the last few years. Excellent geological maps of North America and of Canada have been published recently. No other ^ as per author ltr 23 march 50^ geological map of the Canadian Arctic as a whole has been published for many years. The descriptive parts of this article are largely based upon those papers which are listed at its close and also upon others listed in the bibliographies which they contain. On the mainland most of the work has been done by the Geological Survey of Canada, but information about the Arctic Islands has been gathered by many exploring expeditions. In this paper, wome theories not published in these descriptions are introduced in an endeavor to interpret the history of this part of the earth.

The Major Geological Provinces

Like all continents, North America can be considered to be made up of three types of geological structures. These are exposed shields of disturbed and ancient basement rocks, plains of generally flat-lying, younger rocks

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overlapping these shields, and ranges of relatively young mountains. In North America, the arrangement of these elements is approximately symmetrical. The center of the continent is occupied by the Canadian Shield of basement rocks, which is a comple s ^ x^ of pre-Cambrian rocks representing the eroded and ^ ✓^ leveled roots of former, vanished mountains. It forms a complete ring of moderately uniform width right around Hudson Bay, for pre-Cambrian rocks form the surface of practically all parts of the mainland lying north and east of the Gulf of St. Lawrence, Lake Superior, Lake Winnipeg, and the Mackenzie Great Lakes (Great Bear and Great Slave lakes), and also form most of Baffin Island to the north.

Around these pre-Cambrian rocks in another ring are the plains of the covered shield. These are underlain by fairly flat-lying sedimentary rocks, only a few thousands of feet , thick ^ ,^ resting upon basement rocks. This province ^ ✓^ includes the St. Lawrence River valley, the plains of the north-central United States, the Prairie Provinces, and the Mackenzie River valley a large part of the Arctic Archipelago is also included in this province, for these islands are divided by only shallow arms of the sea.

Sues included most of Greenland in the Canadian Shield, but Baffin Bay is so much wider and deeper than any of the other waters spread upon the con– tinent that it seems probable Greenland should be regarded as a separate continental structure. In any case, our knowledge of those parts is very limited due to great extent of the Greenland ice sheet and ignorance of the geology of the pre-Cambrian rocks of the northeastern Canadian Arctic.

Around the margin of the North American continent are younger mountain ranges. The Cordilleran and Appalachian ranges of folded and faulted sedimentary rocks are arranged in the pattern of an upright V. The Cordillera

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reach the Arctic in the Yukon and Alaska, but the Appalachians are cut off by the sea on the north coast of Newfoundland. In the Arctic, two other ranges of mountains disposed in the shape of an inverted V enclose the northern part of the continent. In comparison with the Cordilleran and Appalachian Mountains, these are neither so large and well known nor so continuous, but they are by no means negligible. The mountains of Northern Ellesmere Island, which form the northwest border facing the Arctic Sea, reach altitudes of 11,000 feet. They extend into Axel Heiberg Island and are perhaps continuous with those which cross North Greenland. According to the view adopted in Canada, the other northern range forms the eastern parts of Ellesmere Island and Devon Island, reaches altitudes of 10,000 feet in Baffin Island, of which it forms the backbone, and continues down the Labrador coast where the range is known as the Torngat Mountains. On the other hand, if Suess’ view be followed, that Greenland is geologically part of North America, the arctic part of the continent is still enclosed by mountains, because another range, rising above 12,000 feet, forms the whole eastern coast of Greenland. If this view be adopted, Baffin Bay and the mountain range through Baffin Island and Labrador would have to be regarded as disturbances within the Canadian Shield. In either case, the continent may be said to be roughly in the shape of a great diamond of pre-Cambrian rocks partly covered by later plains and faced on four sides by higher and younger mountains of which the Western Cordillera are by far the greatest.

This concentric regularity of the continent suggests that it was built by simple, systematic, subcrustal forces, but this article must cut across the divisions into shield, plains, and mountains, and describe only the arctic parts of each. It will deal in turn with the northern parts of the Canadian Shield

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(excepting that part in Greenland), the Paleozoic outliers on the shield, the Arctic Archipelago, the Canadian arctic coastal plains and Interior Plains, and those parts of the Western Cordillera lying within the Yukon. The economic geology of all parts will be treated last.

The Canadian Shield

The Canadian Shield is one of the largest areas of exposed basement rocks in the world. The southern and western parts have been reasonably well covered by geological mapping, but the northern and eastern parts have been examined only along the routes of reconnaissance traverses. Because of the complexity of these rocks, mapping of rock types has greatly outstripped interpretation even in those limited areas which have been well examined. Important summaries of the present state of knowledge have been made by the Geological Survey of Canada, and by Morley E. Wilson and H. C. Cooke. The most recent attempts to interpret structure, using geophysical information, have been made by J. E. Gill and J. T. Wilson.

The annular shape of the Canadian Shield has already been mentioned. Within it, there is further symmetry. The center, in Hudson Bay, is the lowest part and toward it the surface slopes gently inward on all sides. The height of land is generally near the outer margin of the shield. In Baffin Island, mountains as high as 10,000 feet form the rim, while ^ in^ the ^ ✓^ Torngat and Adirondack Mountains the margin is more than 5,000 feet high. Other highlands occur north of the St. Lawrence River and Lake Superior, around the eastern ends of the Mackenzie Great Lakes, along the Coppermine River, beside Bathurst Inlet, on Boothi s ^ a^ Pe l ^ n^ insula, and near Wager Bay. ^ ✓^ Important valleys which cross the rim of the shield are those of the Nelson

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and Ottawa rivers and of Hudson Strait. No heights equal to those common around the rim are reached anywhere in the interior nor around the shores of Hudson and James bays. The shores around three sides of these bays are among the most gently sloping to be found anywhere. Only on the east coast are there any hills. These reach 1,500 feet near Richmond Gulf. There are slightly higher hills inside the western entrance to Hudson Strait.

It is true that Hudson Bay and the region around it were depressed in recent times by ice loading which accentuated the basin shape, but the land has already risen hundreds of feet since the ice melted. It is widely supposed that this rise is still continuing and that Hudson Bay may eventually be drained, but that is by no means certain. There appears to have been little or no rise at Churchill since 1940 when an official and reliable tide gauge was installed. Since the time of Tyrrell it has been the opinion of all Canadian geologists who have examined the field evidence that no rise of the land there has taken place in historical times. In any case, whether this rise continues or not, there is abundant evidence that the central basin is a feature of great antiquity. No future uplift great enough to destroy it has been postulated. The previous existence of this basin in shown by the presser– vation on the islands and around the shores of Hudson Bay of extensive deposits of late pre-Cambrian, Paleozoic, and lacustrine Cretaceous deposits. There appears to have been another smaller basin of deposition in the Foxe Basin.

The nature of the contact between the shield and younger rocks which surround it and lie upon it has not been the subject of close examination in most places. In some areas the contact is an overlap, as it is north of Lake Ontario, but in many other places the contact is faulted. In the interior basin, this seems to be the case on Southampton Island, in Richmond Gulf,

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and south of James Bay. Around the outer margin, there are fault contacts along the St. Lawrence and Ottawa rivers, on Boothi s ^ a^ Peninsula, and perhaps ^ ✓^ in places along the Slave River. The isolated patches of Paleozoic rocks, which are widespread over the shield and which will be described later, are also generally infaulted on at least one side. There is no indication that any of these post-Cambrian fau tl ^ lt^ s are of great magnitude. It is not unusual ^ ✓^ for there to be normal faulting around the margins of sedimentary basins.

A generalized description of the rocks of which the shield is composed in the Arctic is almost impossible. The types are very variable and the areas which have been examined are small. Some principles can, however, be stated with fair certainty.

The first of these is that the same geological processes operated in pre-Cambrian times as have subsequently. There may have been gradual and slight changes so that the conditions under which the earliest rocks were laid down may have been a little different, but there is no evidence of pro– found cataclysms nor of violent disturbances. On the contrary, at intervals all over the shield there is evidence of the operation in these old rocks of those geological processes of erosion, deposition, and glaciations which occur today. There is no evidence of any original crust of the earth, nor much of any unusual rocks except some anorthosite masses. There is no suggestion that the temperature of the surface was not approximately the same as today. For the past two thousand million years it seems to have been between the freezing and boiling points of water at all times. These facts suggest that the different appearance of most pre-Cambrian areas is not because conditions then were different, but because the rocks are older and have been more deeply eroded. The Archean type of rocks of the shield are the roots of vanished.

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mountains, not differing in any marked way except in elevation from the rocks now exposed in the cores of the Cordilleran and the older Appalachian Mountains.

The second principle is that pre-Cambrian time was vastly long and that events occurred during it as complex as those observed in the youngest rocks. The record of these things is now obscured and foreshortened so that there has been a tendency to oversimplify pre-Cambrian history.

Geological evidence and radioactive age determinations both suggest that pre-Cambrian time was much longer, probably at least three times as long, as all subsequent time. When it is remembered that there have been two major post-Cambrian orogenies in the Appalachian and Cordilleran parts of North America respectively, it can be appreciated that there is likely to be evidence of several important periods of mountain building preserved in the pre-Cambrian rocks.

The danger of supposing that pre-Cambrian time is divided into only two great divisions is thus obvious. It has been shown that no universal or even general disturbance nor stratigraphic break marks the close of pre-Cambrian time. Leith has similarly pointed out t r hat no universal break exists between the Archean and Proterozoic (or Algonkian) types or rocks; that properly these are not divisions of time, but rather that they should be used to refer to two types of rock assemblage, the one profoundly disturbed and extensively intruded by granites, the other only gently folded and containing only limited bodies of intrusives. Without doubt, the less altered Proterozoic rocks are often the younger, but that cannot be stated as a general proposition.

This distinction is most important in the Arctic. Although it is convenient to consider the gently dipping Proterozoic type of rocks of the northwestern

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shield, of the Belcher Islands, and of the Labrador Trough together with those which they resemble near Lakes Superior and Ruron, there are no grounds known why they should all be considered to be of the same age nor even why they should all have to be considered late pre-Cambrian in age. Unfortunately, this assumption has often been made.

Because there is a lack of fossils in pre-Cambrian rocks, the few radio– active age determinations will have to be supplemented by a proper understanding of the structure of the shield in order to arrive at even a rough time scale. It is considered that the Archean type of rocks are the cores or roots of old mountain ranges. Fortunately, mountains are built in definite belts and during periods of time limited to a few [: ] hundreds of millions of years. Thus, the coast ranges of the Cordilleran have been built during the past 100 million years while the Appalachian Mountains were folded and intruded by igneous rocks during the Paleozoic period from 200 to 600 million years ago. It is considered that shields can be divided into similar belts which can be roughly dated. In the south and northwest the pattern is emerging, elsewhere it has yet to be discovered.

A third principle which appears to be true is that these mountain belts are concentrically arranged about continental centers or nuclei. The arrange– ment is such that mountain belts generally parallel the margin of the continent with younger rocks toward the outside.

The only exception known to this arrangement parallel to the margin of the continent is the great belt of sedimentary, volcanic, and metamorphic rocks which strike southwest from Chesterfield and Churchill to the margin of the prairie overlap south of Lake Athabaska. So completely does this great belt of rocks appear to violate the rule of arrangement which prevails elsewhere,

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that it has been suggested that the mountains they represent were formed like the Urals, between two old continental masses and the shield started as two centers, one north of Lake Superior and the other north of Great Slave Lake. Greenland likely had a third center and others may be found.

A fourth principle, advanced by Lawson, is that the continents have grown by the formation of these marginal mountain ranges. This is the reason why the provinces become younger toward the margins of continents.

These principles are not yet universally agreed upon and there is a lack of knowledge of pre-Cambrian geology in the Arctic. It is, therefore, not yet possible to subdivide the pre-Cambrian of the Canadian Arctic into belts. One can only give brief notes upon the more outstanding local features of pre-Cambrian rocks of the Arctic.

The greater part of Baffin Island and the eastern portions of Devon and Ellesmere Islands consist of gneisses and granites containing bands of schists, but the rocks of the south coast of Baffin Island include much crystalline limestone, the general assemblage resembling in petrology and in foliated structure that of the Grenville province of the St. Lawrence river valley. In northwestern Baffin Island and in the islands to the north, flat-lying sedimentary beds overlie the granites and gneisses. The lowest of these beds are frequently unfossiliferous sandstones which have sometimes been referred to the late pre-Cambrian and sometimes to the Paleozoic, because the next overlying beds are frequently conformable and contain fossils of Ordovician and Silurian age.

At Arctic Bay, close to Admiralty Inlet, these flat-lying unfossiliferous beds are cut by large basic dikes having a general east-west strike.

The basal complex of Labrador and Ungava consists mainly of gneiss and

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granite, commonly intermixed in different proportions to form migmatites. Rose and there are scattered, clearly recognizable remnants of metamorphosed sedimentary rocks, conglomerates, quartzites, limestones, and schists. Meta– morphosed remains of volcanic tuffs, greenstones, and amphibolites are also found. It is clear that these sedimentary and volcanic rocks were formerly widely spread over that part of the earth’s surface now forming Labrador, but that they have been [: ] extensively transformed into crystalline schists and gneisses and removed by erosion.

Associated with these gneisses in a broad band extending inland from the Labrador coast and from the north shore of the St. Lawrence River are large masses of anorthosite with associated gabbro and other basic rocks. The origin and history of these unusual masses of basic felspar rocks is not yet understood.

Resting upon the basement complex and locally younger than it are several series of much less altered sedimentary rocks. How these are to be correlated with one another and with rocks in other regions is as yet unknown.

At Ramah, near the northern end of the Labrador coast, black slates, quartzites, and impure dolomites rest conformably upon the gneisses and upon basic dikes. Farther south on the coast, similar rocks with a large proportion of interbedded volcanic rocks are known as the Kaumajet series. Other flat-lying or gently folded sedimentary rocks, chiefly cross-bedded quartzites, crop out at intervals around Lake Melville and northwest from it up Naskaupi River as far as Lake Mishikamau.

In the interior of Labrador and Ungava, a belt of younger rocks, known as the Labrador Trough, extends up to 40 miles wide and at least 350 miles long from the head q ^ w^ aters of the Hamilton River to the west side of Ungava Bay. ^ ✓^

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These rocks, which bear a general lithological resemblance to Huronian rocks of Lake Superior district, contain extensive beds of iron formation. They have been thrust-faulted and closely folded with axes in a northwest-southeast direction. To the west, these beds lie unconformably upon gneisses of Grenville type, while to the east, they are succeeded by a belt of predominantly volcanic rocks some 25 miles wide, which, in turn, gives way to granite-gneisses. The volcanic rocks are also faulted but the nature of their contact with the gneisses to the east is still uncertain, although some reconnaissance wor l ^ k^ ^ ✓^ suggests that the gneisses are thrust over the volcanic rocks.

On Richmond Gulf, two gently folded formations are separated by a slight unconformity. The lower formation consists of arkose and sandstone with some basic lavas, while the upper consists of dolomite with algal structures, basic flows, sandstone, slate, and iron formation. These formations are cut by intrusions of diabase. It has been suggested that these beds have all been preserved by subsidence faulting closely parallel with the curved coast of Hudson Bay. On the Belcher Islands, 8,000 feet of beds similar to those in the upper series at Richmond Gulf have been preserved in beds folded in a regular and striking manner. Inliers of diabase and other rocks similar to these crop out through Paleozoic limestones along Winisk and Sutton rivers in northern Ontario. Other flat-lying rocks of generally similar character have been preserved by infaulting around Lake Mistassini and Lake Chibougamau in Quebec.

In the western Arctic, the pre-Cambrian succession is better known and more complete. The oldest known rocks are the Yellowknife series which consist mainly of altered graywackes with basic lavas. They crop out over extensive areas north of Great Slave Lake. They have been correlated with similar rocks

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at Indin Lake, Point Lake, and near Lake Athabaska. They are separated by faulting and unconformity from another younger series of rocks, the Snare group, which is also intensely folded and altered. The Snare group, which extends northwest from Indin Lake to Great Bear Lake, contains ores of radio– active elements which have been shown to be 1,400 million years old. Both are cut and surrounded by great areas of granite and gneiss which is known in some places to be of more than one age. In the East Arm of Great Slave Lake, the Great Slave group is well developed and resembles the Snare group. Both groups consist of thick beds of quartzite, argillite, and dolomite which bear algal structures. South of Great Soave Lake, there are thick beds of arkose and conglomerate called the Nonacho series. They are gently folded, but are cut by some granites. On the north shore of Lake Athabaska, similar rocks are known as the Beaverlodge group.

Along the Arctic coast in the vicinity of Bathurst Inlet are the Epworth dolomite, Kanaryak formation, and Goulburn quartzite. Along the coast these are flat-lying beds cut by granites in at least one place; along Bathurst Inlet they are folded parallel with the inlet up which they extend but their southern limit has not been mapped.

Farther west and possibly of the same age as the Goulburn quartzite, or perhaps younger, the Coppermine series with an estimated thickness of up to 48,000 feet dips gently north along the arctic coast of Coronation Gulf and Amundsen Gulf. The lower rocks are chiefly basaltic lava flows separated by thin beds of conglomerate, while the middle portion is characterized by red and brown sandstones passing upward into red sandstone, shale, limestone, and dolomite cut by diabase sills.

Other gently dipping trap and sedimentary rocks f ro ^ or^ m Kent Peninsula and ^ ✓^

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parts of both the southern and northern coasts of Victoria Island. It has been suggested by O’Neill that all these gently dipping rocks are of similar late pre-Cambrian age and form a gigantic syncline dipping east toward Boothia Peninsula.

Underlying these sedimentary rocks along the arctic coast and in most places in the interior of the Northwest Territories which have been examined, the oldest rocks are granite and gneiss.

In the district of Keewatin, a belt of old, much-folded and altered sedimentary and volcanic rocks of Archean type extend from Chesteffield Inlet southwest to the eastern end of Lake Athabaska. Concerning this belt little has been published, but it is known to contain thick beds of quartzite inter– bedded with basic lavas. These rocks are cut by granites. Overlying these old rocks along the shores of Lake Dubawnt and Thelon River are flat-lying white and red sandstones. The boundaries of these areas of younger rocks are not yet well established, but they are generally similar to the rocks cropping out over a large area south of Lake Athabaska.

Palezoic ^ O^ utliers on the Canadian Shield.

The center of the Canadian Shield is now occupied by Hudson Bay, but around its shores are preserved areas of Paleozoic rocks which show that the depression is of great antiquity and not solely a result of incomplete recovery from isostatic sinking under a Pleistocene ice sheet. The two main areas in which these rocks are now exposed are in the Hudson Bay lowland, which extends along the southwest coasts of Hudson and James bays, and on several islands in the northern part of Hudson Bay.

Large areas of Paleozoic rocks are also preserved around the shores of Foxe Basin. Akpatok Island in Ungava Bay consists entirely of Paleozoic strata.

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Small outliers have been found at many scattered places across the Canadian Shield.

The Hudson Bay lowland borders James Bay on the south and west and extends along Hudson Bay as far west as Churchill. It is a low, nearly featureless plain, with a seaward slope of less than four feet per mile which continues out under James Bay, forming an intertidal zone as much as several miles wide. The plain is covered with drift and muskeg so that rock outcrops are mainly along river banks and occasionally on the coast.

South of James Bay, the contact of the Paleozoic limestones with the older pre-Cambrian rocks may be faulted, for the margin of the basin rises in an escarpment down which the several tributaries of the Moose River descend in a series of falls and rapids.

According to the Geological Survey of Canada, the oldest sedimentary rocks are the Nelson River and Shamattawa limestone formations, together 150 feet thick. These have been correlated with Red River and Ston e y Mountain forma– tions of the Lake Winnipeg region. Formerly, they were regarded as Trenton (Middle Ordovician), but they are now classed as Richmond (Upper Ordovician), although some Trenton fossils recur. This has led to confusion. The Lower and Middle (Niagaran) Silurian epochs are represented by about 300 feet of limestones. These are overlaid by about the same thickness of Devonian rocks divided into five formations representing all three epochs of that period. They have been correlated most closely with formations of New York State.

In two small areas there are lacustrine deposits of clay, sand, and lignite, probably of Lower Cretaceous age.

Diagonally across Hudson Bay are other important areas of Paleozoic rocks. Southampton Island may be divided into two parts, of which the larger southwestern

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portion is a lowland underlain by Upper Ordovician (Richmond) and Middle Silurian (Niagaran) rocks. These are separated, probably by faulting, from the northeast plateau of granite and gneiss. According to Manning, one patch of limestone has been preserved near Seahorse Point on this plateau at a height of several hundred feet above the main limestone plain to the southwest.

In the entrance of Hudson Strait, southeast of Southampton Island, are Coats of ^ and^ Mansel Islands, each a low flat plain underlain by limestone, ^ ✓^ probably similar in age to that on Southampton Island. A ridge of pre-Cambrian gneiss crosses the northern end of Coats Island.

The shores of Foxe Channel, which leads north from Hudson Bay, are all of pre-Cambrian age, but to the north much of the coast line of Foxe Basin con– sists of Paleozoic rocks.

In the Putnam Highland, which lies west of Amadjuak Lake and north of Foxe Peninsula on Baffin Island, Gould has described 600 feet of unfossiliferous shale which rests upon pre-Cambrian gneiss and schists intruded by some granite. The shale is overlain by 100 feet of limestone containing a rich fauna. Both Hussey and Foerste have stated that this is typical Arctic Richmond. Soper also made collections on Baffin Island which have been examined by Alice Wilson. She agrees with the correlation with Red River (Richmond) formation, but has found some Collingwood (Middle Ordovician) fossils as well.

On the east shore of Amadjuak Lake and again on Silliman Fossil Mount, a small outlier near the head of Frobisher Bay, the same Arctic Richmond fauna has been found.

On the north coast of Foxe Basin are several large islands and peninsulas underlain by Paleozoic rocks, while a large part of Melville Peninsula and of the adjacent islands are underlain by shaly limestone from which Richmond faunas

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have been identified.

Akpatok island is an isolated island in Ungava Bay. It is 550 square miles in extent and cliffed all around its shores. A large collection of the fauna was made by Cox and carefully studied by him and others. It is considered to be Arctic Richmond corresponding to Nelson River and Shamattawa formations of Manitoba. Some of the trilobites have some relation to those of the Utica formation of Middle Ordovician epoch.

In addition to these main outliers, there are a large number of small ones. The best known of these are the Ordovician and Silurian outliers which extend up the Ottawa River valley as far as Lake Nipissing and Lake Timiskaming where Richmond and Niag ^ a^ ran limestones are preserved. There ^ ✓^ are also four or five small occurrences in Quebec, all of Ordovician age. These are at Lake St. John and at Arvida on the Saguenay River, at Lake Waswanipi p at the headwaters of the Broadbak River and at Lake Manikouagan on the river of the same name. There are several reports of loose blocks with Collingwood fauna from near Cape Chidley at the north end of Labrador.

The most isolated occurrence was reported by J. B. Tyrrell who collected Richmond fossils from Limestone Island on Lake Nicholson near Lake Dubawnt, in the heart of the Northwest Territories west of Hudson Bay.

It is now possible to summarize the Paleozoic and subsequent history of the Canadian Shield.

Outliers of Paleozoic age are widespread over the Canadian Shield. These are all flat-lying and generally downfaulted. Only a few formations are represented. Of these, Arctic Richmond (Upper Ordovician) corresponding to the Nelson River and Shamattawa formations of the Hudson Bay lowland and to the Red River and Stony Mountain formations of Lake Winnipeg region is the

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most widespread. Great confusion has been caused in the literature by the fact that these formations were at one time correlated with the Middle Ordovician (Trenton) of eastern Canada. Other formations found in several places are the Middle Ordovician (Collingwood) and Middle Silurian (Niag ^ a^ ran). ^ ✓^ Devonian and lacustrine Cretaceous formations have been found only near James Bay. The fact that flat-lying remnants of a very few formations have been found so widely and that the great majority of epochs and periods are not represented at all plainly suggests that the Canadian Shield was a low plain throughout this great interval, that it was exposed in the Cambrian period and most of the time subsequently, and that it was only occasionally and for short intervals covered by shallow seas. At some time since the Devonian, possibly at the time of the Appalachian revolution, the shield underwent slight normal faulting.

The Canadian Shield thus generally formed an effective barrier to the migration of marine life between the Arctic and the rest of North America. It is therefore, not surprising that A ^ a^ rctic faunas can more often be ^ ✓^ correlated with those from western North America or from Europe than they can with those of the eastern and central United States and southeastern Canada.

The Arctic Archipelago

The Canadian Arctic Islands form an unique assemblage of large islands separated by comparatively narrow channels and fjords whose pattern is in some parts almost rectilinear and elsewhere gently curved. Nowhere is there another group of islands so peculiarly divided. No other archipelago except Oceania contains so many large islands. Indeed, it is seldom realized how huge these islands are. Baffin Island, which is nearly 1,000 miles long, would reach from Ontario to Florida. Three of the islands are each larger

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than England. In view of their size, inaccessibility, and the present lack of economic incentive, it is not surprising that their interiors are largely unexplored, but from a scientific viewpoint it is unfortunate that the whole interesting area is so little known. Although the pattern suggests that the islands may be partly divided by faulting, it would be interesting to know how this could have occurred without causing more disturbance tha t ^ n^ is evident ^ ✓^ on the existing maps.

The archipelago forms a great flat basin of covered shield, mountainous in the north but open to the Arctic Sea on the west and resting to the south and east upon Archean rocks of the mainland and of Baffin, Devon, and w^s^outh– east Ellesmere Islands. The prominent rocks in the basin are pre-Cambrian quartzites, Ordovician, Silurian, and Carboniferous or Permian limestones with lesser outcrops of other Paleozoic, Triassic, and Tertiary sedimentary rocks.

The general geology of the islands of the Arctic Archipelago has been described and mapped on a small scale by the Geological Survey of Canada, but the detailed geology is known in only a very few small areas. Systematic mapping of the region has hardly begun. Only a general account of the geology can be given and that may require modification by subsequent more detailed exploration.

The chief cause of this uncertainty is that, although systematic explora– tion of the northern islands may be said to have been begun by Parry in 1820, the first extensive geological work to be done was that by Schei between 1898 and 1902. Few expeditions have been accompanied by geologists, and fossils brought back on many other expeditions may have often been picked up loose or, if collected from cliffs, the specimens from different horizons may have been mixed. Some of the older collections were described by contemporary geologists

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who used names no longer current; others were not described until as much as a century after they had been collected. The importance of the Canadian Shield as a barrier was not at first understood by the paleontologists who described the collections. They did not in all cases realize that the fauna of the Arctic Archipelago was thus isolated from the developed differently from the faunal assemblages to which they were accustomed. It will thus be understood that the limited knowledge available has been reduced in value by an element of confusion and uncertainty.

The formations exposed in the Arctic Archipelago are successively younger from the edge of the Canadian Shield toward the northwest. The formations also thicken in that directions, so that the most complete sections have been measured on Ellesmere Island, where the Paleozoic strata alone have a thickness of at least 10,000 feet. As these rocks in the northern islands have been studied by competent geologists, it will be convenient to describe them first.

The Mountains of Northern Ellesmere Island . In the extreme northern parts of Greenland and Ellesmere Island there are high mountains, believed to reach 11,000 feet in Ellesmere Island and 6,000 feet in Greenland. These mountains are divided by Kennedy and Robeson Channels, which have a minimum width of about 13 miles, and by several large fjords which penetrate the north coast of Greenland. Parts of them have been called the Challenger, United States, and British Empire ranges, and other names by different explores, but the extent of and divisions between these ranges is not yet known. From the air, the northern part of Ellesmere Island appears as a complex of peaks deeply [: ] dissected by glacial erosion and still to a large extent engulfed by ice which fills the valleys. The mountains continue across Nansen Sound into Axel Heiberg Island. On the east and west coasts of that

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island are ranges of mountains rising to 7,000 feet. Between them is an unbroken icecap which is about the same elevation and from which glaciers flow to fill the valleys. Here the mountains end, for the Ringnes Islands are not over 1,000 feet in altitude.

Very few of the peaks on any these islands have been climbed or even seen except from the air. The area constitutes one of the least known and most fascinating regions in North America.

The very limited studies that have been made show that these mountains are composed of schists, slates, sandstones and limestones lying in folds with axes striking northeast and southwest. Granite pebbles have been picked up by both the expeditions that have explored the north coast of Ellesmere Island, but the age of the intrusive and of the sedimentary rocks in the mountains is unknown.

Sch i ^ u^ chert suggested that in Proterozoic time a geosynclines, which he ^ ✓^ named Franklinian, formed striking northeast across these islands and northern Greenland. He believed that its sediments were derived from an active rising land mass, Peary Land, which at that time lay to the north. Teichert, however, has suggested that the Canadian Shield was the source of the sediments. Very recently, Eardley has again postulated that the whole basin of the Arctic Sea was filled by a land mass, Ancient Arctica, which started to sink only in Carboniferous time. The geological arguments he advances are not convincing and may have some other explanation. He suggests no physical reason nor mechanism for depressing a vast area by at least 15,000 feet while the adjacent Canadian Shield remained quite stable. The proposal runs counter to all seismic, isostatic, and other physical evidence. In fact, from a geophysical viewpoint it seems hardly possible that

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the whole area of the arctic basin sank as recently as he has suggested, but it is probable that there have been extensive alterations of shore lines within the limits of the shallow continental seas. These may be regarded as sufficient to answer the geological arguments he has put forward.

There is no doubt, however, that throughout Paleozoic and Mesozoic times there was in those parts a geosynclinal or marginal sea in which a great thickness of deposits was laid down. No section has been measured within the area of folded mountains but south of them along both coasts of Ellesmere Island excellent exposures have been studied, especially by Schei and Bentham.

Ellesmere and Axel Heiberg Islands . Pre-Cambrian gneiss and schist cut by granite, syenite, and gabbro are exposed along the coast of the southeastern quarter of Ellesmere Island and have also been observed at the head of Bay Fjord in the center of the west coast. Along the south coast these rocks are characterized by a high content of hypersthene.

Overlying the gneiss at Bach Peninsula in the center of the east coast are 400 feet of red and white unfossiliferous sandstones resting upon a flat erosion surface. These rocks resemble the Thule sandstone in Greenland, are cut by diabase sills, and pass upward conformably into about 3,000 feet of shales and limestones containing Middle or Upper Cambrian and Lower Ordovician fossils.

North of Bache Peninsula and on Bay and Vendome Fjords on the west coast and near the center of the south coast are exposures containing the well-known Arctic Richmond fauna which is widespread through the Canadian Arctic. This has been correlated with the Red River fauna of Manitoba and the Cape Cal b ^ h^ oun ^ —^ of east ^ west^ Greenland, but, confusingly enough, was generally called Trenton until 1920.

Both in Kane Basin on the east coast of Ellesmere and on Goose Fjord in the southwest, dark shale and limestone containing the Lissatrypa phoca fauna follow. These beds have been referred both to the Silurian and to the Devonian, but Foorste places them in the basal Devonian in spite of a survival of a great percentage of Silurian fossils. This is a northern fauna which is found in a belt from north Greenland as far south as Boothia Peninsula, but which is nowhere found together with the Niag ^ a^ ran (Middle ^ ✓^ Silurian) fauna which only reaches as far north as Southampton and King William Islands.

In southwestern Ellesmere Island these are succeeded by 950 feet of unfossiliferous shale and sandstone which pass upward into 1,600 feet of richly fossiliferous shale and limestone containing Lower, Middle, and Upper Devonian formations. These pass upward into 2,000 feet of sandstone contain– ing Upper Devonian plant remains. Similar Devonian beds crop out along the fjords of the west coast and on Devon Island. Holtedahl has described Schei’s collections from these areas. Unfortunately, the succeeding beds were nowhere examined, but on Bear Cape in southwest Ellesmere Island collections were made from a limestone containing a rich fauna corresponding closely to that called Upper Carboniferous in Russia, although it would be classed as Permian in America. This is another formation widespread in the Arctic. It also occurs in northeastern El ^ l^ esmere Island, at the north end of Axel Heiberg Island, and ^ ✓^ in Peary Land in n ^ N^ orth Greenland, as well as widely in the Parry Islands. ^ ✓^

The chief known area of Mesozoic rocks in the Canadian Arctic is on both shores of Eureka Sound, which separates Axel Heiberg from Ellesmere Island. These shales contain both marine and plant fossils, both probably of Middle Triassic age and related to that of Sp ti ^ it^ sbergen. In the same area are local ^ ✓^

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deposits of thick light-colored sandstone, shale, and layers of lignite of Miocene age.

Between the deposition of these two formations very numerous diabase dikes and sills were intruded. They are probably of the same age as other diabase intrusives on the eastern and southern coasts of Ellesmere Island and on Ellef Ringnes Island.

The basic intrusives accompanied mountain building of late Mesozoic age, for the Triassic beds were steeply folded before the undisturbed Cenozoic beds were deposited. It is possible, but not certain, that this was the orogeny that formed the mountains of northern Ellesmere Island.

Some indefinite evidence of an earlier period of folding has been found in three areas. About 100 miles south of Eureka Sound ^ ,^ in the southwestern ^ ✓^ part of Ellesmere Island, folded Ordovician and Silurian rocks crop out along the north coast of Baumann Fjord. On the south side of the fjord are com– paratively undisturbed Devonian and Carboniferous limestones. Bentham ^ ✓^ believed, bu r ^ t^ could not prove, that these overlie the earlier strata on the opposite side of Baumann Fjord, indicating a Caledonian or late Silurian disturbance in the area lying immediately to the southeast of the Mesozoic ranges.

The interior of Ellesmere Island has never been examined, but on its northeast corner, 300 miles diagonally across the island, are the folded and unfossiliferous Cape Rawson beds which Bentham and Koch believed to be a continuation of the Silurian beds in Baumann Fjord. Fielden had found these Cape Rawson beds to pass beneath flat-lying Carboniferous strata, but did not observe the contact, which may be an overthrust. Koch supported his correlation by identifying with the Cape Rawson beds other folded and metamorphosed

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rocks which occur across Kennedy Channel in Greenland and from which he reported doubtful Silurian Fossils. Schei, on the other hand, believed the Cape Rawson beds to be a continuation of the Triassic beds he studied in Eureka Sound, and that, therefore, no evidence had yet been found for any but post-Triassic folding and mountain building, but he did not deny that evidence for earlier orogenies might yet be found. In any case, the Plaeozoic strata toward the southeastern part of the island are only gently folded, but probably underwent faulting during the Tertiary period.

The Parry Islands. These islands form the central part of the archipelago. The largest of them are Prince Patrick, Melville, and Bathurst Islands, all of which are fairly flat islands with broken or cliffed shore lines up to 1,000 feet high. The greater part of them, of the small islands around them, and of the adjacent peninsulas or Cornwallis and Devon Islands are underlain by flat-lying rocks of probable Permian age. These consist of 1,000 feet of shales overlain by the “sandstone series” and “limestone series” of greater thickness. White sandstones containing thick seems of coal and both fossil plants and invertebrates crop out on the south coast of Melville Island and over most of Bathurst Island. The younger “limestone series” has been found on Grinnell Peninsula of Devon Island and on the north coasts of Bathurst and Melville Islands.

The fossils in both series have been ascribed to the Carboniferous and resemble and Upper Carboniferous of Russia, but are generally regarded as more closely allied to those of Permian age in the United States. Volcanic rocks of probably the same age occur in southeastern Bathurst Island.

Mesozoic marine fossils have been found on Prince Patrick and Bathurst Islands, and fossil wood of Miocene age on w ^ s^ outhwestern Prince Patrick Island. ^ ✓^

A few fossil ammonites have been brought from the Ringnes Islands and from those discovered by Stefansson. These fossils and the similar topog– raphy make it appear likely that they are underlain my Mesozoic and perhaps Permian rocks similar to those on Axel Heiberg and the Parry Islands.

Devon, Cornwallis, and Somerset Islands. The eastern part of Devon Island is underlain by pre-Cambrian granite and gneiss rising above 3,000 feet and covered by a small icecap. The pre-Cambrian surface dips toward the western part of the island, where it is overlain by a succession of younger beds which form magnificent cliffs of gradually decreasing height. On the north coast, Cambrian, Arctic Richmond (Upper Silurian), and Devonian formations have been definitely identified, while Grinnel Peninsula which extends to the northwest is underlain by flat-lying Permian of the “sandstone series.” On the south coast, the cliffs have generally been described as Silurian in age, but a large part of them contain the Lissatrypa phoca fauna whose age is disputed and may be basal Devonian. Shaly limestones containing the same fauna probably underlie most of Cornwallis Island except the northern tip.

A ridge of pre-Cambrian gneiss extends north from Boothai Peninsula along the west coast of Somerest Island, but the greater part is underlain by a plateau of flat-lying Ordovician and Silurian or Devonian limestones which form cliffs up to 1,000 feet high. Fossils of the Arctic Richmond and Lissatrypa phoca faunas have been found around the north, east and south coasts.

Boothia Peninsula, Prince of Wales Island, and King William Island. A rugged and unexplored ridge of pre-Cambrian rocks forms the greater part of Boothia Peninsula and extends northward to underlie the west shore of Somerset Island and the east coast of Prince of Wales Island. The southern arctic

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islands are thus divided into two basins of Paleozoic rocks, but too little is known of the rocks which they contain to be able to state whether there are significant differences between them. Along the east coast of Boothia Peninsula, Richmond (Upper Ordovician), and Lissatrypa phoca (Silurian or Devonian) faunas have been found. Inland, granite cliffs rise up to 1,500 feet above these limestones, suggesting that the ridge has been upfaulted. On the west coast of Boothia Peninsula fossils from the same two formations as on the east coast have been identified. According to Foerste this is the most southern occurrence of the Lissatryp o ^ a^ phoca fauna. ^ ✓^

To the southeast, the Simpson Peninsula is also underlain by undifferen– tiated Paleozoic limestone which has also been described as being faulted against granite gneiss.

Very little is known of the geology of Prince of Wales Island. Except along the east coast where pre-Cambrian rocks occur, it is low and underlain by limestone from which Silurian fossils of unknown period have been reported.

King William is an extremely flat, low-lying island covered with a multitude of lakes. At the western end of it, fossils of Upper Ordovician age have been collected by Washburn as well as earlier explorers. Middle Silurian (Niag ^ a^ ran) fossils were collected by Rasmussen along the south coast. ^ ✓^

Victoria Island . Only the south coast and western part of this great island have yet been explored. The geology is chiefly known from the reports of O’N d ^ e^ ill and Washburn, although the island has also been examined by ^ ✓^ several parties of prospectors.

O’Neill suggested that the rocks of the Coppermine series of late pre-Cambrian age formed a great syncline whose parallel limbs extended across northern and southern Victoria Island and met on the mainland west of Dolphin

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and Union Strait. Certainly in all these areas there are gently dipping sedimentary series of great thickness, cut by diabase sills and containing basalt flows. The basal strata are predominantly reddish sandstone and conglomerate, but are more calcareous toward the top, where dolomite beds contain the digitate forms of stromatolites (gymnosolen) which have been described by Cloud.

Between the north and south limbs of this easterly plunging syncline, and especially on the west coast of Wollaston Peninsula, around Prince Albert Sound, and on Read, Sutton, and Liston Islands in Dolphin and Union Strait there are Upper Ordovician and possibly Silurian limestones. There may be limestones of the same ages at places along the south and southeastern coasts.

Sedimentary rocks containing coal have been reported from the northwest coast of Victoria Island on the shore of Prince of Wales Sound. The presence of coal indicates a post-Silurian age, probably Permian, since strata of that age containing coal are known to occur on Banks and Melville Islands nearby. The strata may, however, be in part Tertiary in age.

The Princess Royal Islands, between Victoria and Banks Islands, have been classed as Silurian or Devonian on the basis of a single fossil collected by M’Clure and preserved. Washburn favors a Devonian age on account of descriptions of coal and petrified wood on the islands, but admits that there is no certainty that these latter came from the same horizon as the fossil.

Banks Island . The stratigraphy of Banks Island is very little known except that limestone, sandstone, and coal of probable Permian age occur along the north coast where they were described by Alexander Armstrong in 1857.

Stefansson found coal a little south of the center of the island which from his description is almost certainly of Tertiary age. Other loose pieces

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of coal which may be of any post-Silurian age have been found at several localities. As a result of assigning these occurrences to different ages, the various authorities have produced maps which show a wider disagreement in the geology of Banks Island than for any area of similar size in the Canadian Arctic.

From the striking cliffs at Nelson Head, in the extreme south, the land rises steeply to 3,000 feet or more to form the highest land in a very large region. On lithological grounds these rocks have been assigned to the Coppermine series, but Washburn has indicated the uncertainty of this correlation.

The Arctic Coastal Plains and Interior Plains

The wide plain which forms the arctic coast of Alaska narrows toward the International Boundary, where it is only about ten miles wide between the Richardson Mountains and the sea. It immediately broadens in Canada and merges up the Mackenzie River valley with the Interior Plains of North America. The western boundary of this province is the border of the Canadian Shield. This extends from Darnley Bay on the arctic coast southward through Great Bear and Great Slave lakes.

The only truly arctic part of the Interior Plains province is a narrow strip along the coast, in which outcrops are scarce and which has been little studied. A large part of it is covered by alluvial deposits of the Mackenzie River delta.

The boundary with the Canadian Shield is very poorly exposed between the arctic coast and Great Bear Lake, where its position has best been determined by Bateman who made a reconnaissance survey for that purpose. From Great Bear to Great Slave Lake the contact of flat-lying Ordovician shale and dolomite with underlying granite-gneiss is well exposed along a chain of lakes. Farther west,

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Silurian rocks have been found north of Great Slave Lake and underlie the Mackenzie lowlands. They have been best studied in the vicinity of the oil field at Norman Wells, there 1,500 feet of hard, dolomitic limestone inter– bedded with anhydrite and shale have been included in the Ronning group. This is overlain by 400 feet of brecciated dolomite of uncertain age. These are succeeded by Middle Devonian strata.

No strata of Lower Devonian age have been recognized in the Mackenzie valley region, but the Middle Devonian is represented by as much as 3 ^ 2^ ,000 feet ^ ✓^ of limestone and shale which is succeeded by Upper Devonian deposits of shale, limestone, and sandstone. These beds thicken to as much as 3,000 feet in the northern part of the valley, where shale predominates. The Devonian strata thus form an important part of the section in the Mackenzie River valley and occupy a wide belt along the entire course of the Mackenzie River except where they are overlain by Cretaceous beds or thick alluvium.

No beds of any age from Carboniferous to Jurassic have been found in the Mackenzie River valley, but it is not known whether this is due to erosion or whether beds of these ages were never deposited. In any case, Cretaceous strata rest directly upon Devonian beds in many places and overlap onto the edge of the Canadian Shield north of Great Bear Lake, which they surround on all shores except the eastern. During the Lower Cretaceous epoch the southern part of the Eastern Cordillera was a land mass, but north of Athabaska River to the arctic marine shale of the Sans Sault group, nearly 4,000 feet thick, rests on an eroded surface of Devonian rocks. In the vicinity of Norman Wells, the Upper Cretaceous is 2,500 feet thick and has been divided into three formations, which, in ascending order, are the Slater River, Little Bear, and East Fork. The Slater River is formation, which rests upon the Lower Cretaceous Sans Sault

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group, is composed of black fissile shale with a few thin beds of bentonite. The Little Bear formation consists of sandstone, shale, and lignite of alter– nating brackish and fresh-water origin, while the East Fork formation consists of gray marine shale. Farther north, extensive deposits of Cretaceous age which have not been studied in detail emerge from either side of the Mackenzie delta to fringe the arctic coast. Recent work by Bostook suggests that they underlie only a narrow strip of the north Yukon coast, and that the Paleozoic rocks of the Richardson Mountains approach the cost more closely than is shown on existing maps.

Resting unconformably on the Upper Cretaceous in a small area around Fort Norman are shale, soft sandstone, and conglomerate of Paleocene age. These beds attain a maximum thickness of about 1,600 feet and contain seams of coal up to ten feet thick. Other small areas of Tertiary strata occur on the coast of Darnley Bay and in the valleys of the Porcupine and Red rivers.

The western border of the Interior Plains province is marked by the rise of the foothills of the Cordilleran province.

The Cordilleran Region .

The eastern part of this province is the only one that enters the arctic regions and there it is divided into the Richardson, Mackenzie, and Franklin ranges which are the northern counterparts of the Rocky Mountains. Only the northern end of the Richardson Mountains reaches the true Arctic.

The Richardson Mountains extend south from the narrow coastal plain opposite Herchel Island, near the Alaskan boundary, as a nearly straight range up to 5,000 feet in height, more than 40 miles wide, and nearly 200 miles long. They truncate the east-west ranges and structures that prevail across

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the northern part of Alaska, but the geology of the hinterland between them in northern Yukon has scarcely been examined. Indeed, most of the structure of the Richardson Mountains has been interpreted only from a study of air photographs by Bostook.

Southeast of the Richardson Mountains is the Peel Plateau, a triangular plain rising in a scarp several hundred feet above the Mackenzie valley. It is crossed by the entrenched valleys of the Peel and Arctic Red rivers. South of this plateau stretch the Mackenzie Mountains in a broad crescent rising abruptly from the Interior Plains. They consist of well-stratified ridges of sedimentary rocks, without intrusives and are reported to rise as high as 10,000 feet. Across the Mackenzie River, and between it and Great Bear Lake, is the narrow range of the Franklin Mountains which rise at Fort Good Hope and for 400 miles to the south parallel to the river and never more than 30 miles wide. The highest peaks reach 5,000 feet.

All these ranges were folded at the same time out of the same geosynclinal basin so that it will be convenient to treat their stratigraphy together. The few igneous rocks yet found in the Eastern Cordillera are confined to the ranges farther south.

Unfossil ^ if^ erous strata thought to be of late pre-Cambrian age have been ^ ✓^ found in the Franklin and Mackenzie Mountains. These are overlain by shale and sandstone at least 200 feet thick in which Middle Cambrian fossils have been found. It is doubtful if Lower and Upper Cambrian are represented in these ranges.

Limestone of Upper Ordovician age have been found in the Mackenzie Mountains, containing a Richmond fauna similar to that so widespread in all Arctic Canada. Silurian beds are well exposed in the Franklin and Mackenzie Mountains, forming the chief part of the former.

No Lower Devonian strata have been identified in any part of the Rocky Mountain region, but up to 2,000 feet of limestone and shale of Middle Devonian age and 3,000 feet of Upper Devonian shale, limestone, and sandstone form an important part of the section in the Mackenzie valley and in the Mackenzie Mountains.

Carboniferous and Permian rocks occur along the Liard River and Alaska Highway but have not been found in the Mackenzie valley region. Triassic rocks also thin out and are not found far north of the Liard River, but they do reappear on the Alaska boundary between the Porcupine River and the arctic coast. Jurassic strata have not been found between the Alaska Highway and the Richardson Mountains, but marine Jurassic beds have been found in that range and along the Firth River near the Alaska boundary. Cretaceous rocks have not been found in the Mackenzie Mountains, but, according to the Geological Survey of Canada, occur on the Peel Plateau on the banks of the Arctic Red and Peel rivers, in Richardson Mountains, and on Porcupine River to the west, but have not yet been studied in detail.

In the early part of the Tertiary period and perhaps earlier in the north, the thick deposits of the Rocky Mountain geosyncline were folded and large blocks wee thrust eastward. The Mackenzie and Franklin Mountains were subjected to broad folding with subordinate thrust faulting which produced their arcuate shape. No detailed work has been done in the Richardson Mountains, but they are reported to be characterized by straight north– trending folds.

Economic Geology

The question of the possibility of economic development of the arctic regions is frequently raised. As far as mineral and oil production is concerned,

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the answer is no longer problematical, for in Canada several mining areas and one oil field are already in economic production in the subarctic close to the border of the arctic regions and it is only a matter of time until some of the mineral resources known to occur in the Arctic are brought into production also. There has been a rapid northward spread of mining activity which has temporarily been halted by the increased costs incidental to operations beyond the tree line. Every year some prospecting is done and some claims are held within the Arctic. The most northern of the Canadian subarctic mining areas and the prospects of developing camps beyond them will be discussed from west to east.

Until the recent discoveries of oil near Edmonton (see articles on bituminous sands of northern Alberta), Canada’s second largest oil field was the one at Norman Wells, on the Mackenzie River about 90 miles south fo ^ of^ the ^ ✓^ Arctic Circle. Since it was discovered in 1920 by drilling in the vicinity of oil seeps, this field has supplied oil to a local refinery to serve the requirements of the district. In 1942, development was accelerated by the Alaska Highway and Canol projects which resulted in the drilling of about 60 productive wells and the construction of a pipe line to Whitehorse, where a refinery was supplied with 3,000 barrels of oil from Norman Wells daily for a short period. As a result, the production rose to 1,200,000 barrels of crude oil in 1944, but with the end of the war and the abanoning of the Canol Project in 1945 it was reduced again to serve only local consumption in the Mackenzie River valley. (See “Development of Oil Fields in Canada’s North.)

The Norman Wells oil occurs in a reef limestone of Upper Devonian age at a depth of from 1,000 to 2,000 feet. Petroliferous shales and oil seepages are widespread in the district so there is a probability that other fields

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are hidden, but so far neither geological nor geophysical methods have been able to locate any of them. Farther north, the arctic coastal plain, although narrow in Canada, offers possibilities, for it is underlain by Cretaceous strata similar to those in which oil has been discovered near Point Barrow in Alaska.

On the east shore of Great Bear Lake, a few miles south of the Arctic Circle, is the Eldorado mine at Port Radium. Before the war, the value of production had reached one million dollars a year, mostly in radium, of which the mine was one of two major world sources. In 1944, this property was taken over by the Canadian Government and for some years its output and activities have been secret. The mine has since been stated to be a major source of uranium for atomic energy. At the time it was discovered in 1930, several other prospects for uranium, silver, and other metals were reported in the same general area but no others were developed.

Northeast of Great Bear Lake, along the Coppermine River and Bathurst Inlet, is a great thickness of late pre-Cambrian sandstone with interbedded lava flows and intruded sills and dikes of diabase and gabbro, all dipping gently north. At many places these beds contain native copper and chalcocite, which has attracted prospectors at intervals since 1771. Large blocks of claims have been held at times. Between 1944 and 1946, extensive geological and drilling exploration was carried out at many places in the Coppermine area but it was found that the deposits could not yet be profitably developed.

On the north shore of Great Slave Lake, and hence some distance from the Arctic, is Yellowknife, now in process of becoming one of the largest gold– mining camps in Canada. Although gold was first discovered in the vicinity in 1898, production did not begin until 1938 and the chief development has

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taken place since 1945. The country rocks are lavas and tuffs, ranging in composition from rhyolitic to basaltic, interbedded and overlain with sediments which are chiefly impure quartzite. The rocks of the Yellowknife group are isoclinally folded and have been intruded and metamorphosed by granite batholiths. They are cut by two important sets of later faults. The important ore bodies are in wide shear zones, striking north-northeast and up to 150 feet wide. Northeast of Yellowknife gold has been discovered near Courageous, Mackey, and Point Lakes and also near the headwaters of the Back River at Began Lake. Besides gold, certain rare elements occur in pegmatites in the same region. From specimens found by natives it is sus– pected that other pegmatites occur near the west end of Contwoyto Lake.

In the years 1928 to 1930, the District of Keewatin that lies west of Hudson Bay was the scene of active and widespread prospecting by four companies. Although the only production that resulted was from a pocket a gold on the coast of Term Point, interest has never entirely ceased, and a wide belt of Archean sedimentary and volcanic rocks, which extends for five hundred miles southwest from Rankin Inlet, has been prospected form time to time since. Several blocks of claims, including a nickel deposit at Rankin Inlet, have been held for many years. Another belt of volcanics and iron formation at Baker Lake, also known for many years, was again prospected in 1946.

In Labrador, the main interest has been in the subarctic where very large deposits of high-grade iron ore are now being developed in a belt of late pre-Cambrian sedimentary rocks. This belt extends north to the west of Ungava Bay where it is being prospected, but the richest ore bodies reported to date have been from the southern part of the belt and there has been no announcement of plans to develop properties in Ungava. Other sedimentary

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and volcanic belts in Ungava have been prospected. There has been interest in lead and iron deposits at Richmond Gulf, while iron deposits on the Belcher Islands have been examined without success.

On Baffin Island, Frobisher Bay was the scene of the first prospecting in Canada, in 1576-1578, but the reputed gold was found to be worthless pyrite and there has been no production from any part of Baffin Island except for insignificant amounts of graphite and mice. In 1945, prospectors examined a number of conspicuous gossans in southern Baffin Island, which had been seen during the war, but could only find rusted gneisses. The area generally held to be most interesting is in the vicinity of Arctic Bay, where minerali– zation was reported by Bernier and where claims were staked in 1937. Lignite is mined for local use in Tertiary beds at Pond Inlet.

In the other Arctic Islands little prospecting has been done. Oil seeps have been reported on Melville Island and coal on many islands. Concerning the possibility of obtaining coal for local use on the islands, Mackay has stated that estimates must be regarded simply as wild guesses due to the meager data pertaining to the various occurrences. Most of these occurrences are of float coal, but in a number of the islands several such occurrences have been reported so that it appears fairly safe to assume that the coal is of local origin and probably underlies a considerable area.

It will thus be appreciated that the geological study of the Canadian Arctic has scarcely begun. Since the war, improved means of transport and the establishment of permanent meteorological stations has greatly facilitated access to these regions. The important economic developments at Norman Wells, Eldorado, Yellowknife, and in Labrador, although all in the subarctic, have stimulated prospecting and geological surveying within the Arctic.

J. Tuzo Wilson

	Page
Introduction	1
The Major Geological Provinces	3
The Canadian Shield	6
Palezoic Outliers on the Canadian Shield	15
The Arctic Archipelago	19
The Arctic Coastal Plains and Interior Plains	30
The Cordilleran Region	32
Economic Geology	34
Bibliography	39

Geology of Arctic Canada: Encyclopedia Arctica Volume 1: Geology and Allied Subjects