GEOLOGY OF ISLAND GROUP II.
This group is comprised of the great island of Baffin, with Bylot island lying off its northeast corner, and the many smaller islands which lie as a fringe around both.
Geological specimens from the east side of Baffin were collected by the expedition under Ross and Parry, and were described by Dr. McCulloch. They consisted of loose specimens collected in two localities, and give little information. Specimens collected by Parry on the same coast were described by Koning as gneiss and micaceous quartz rock, also some ambiguous granitic compound in which hornblende seems to enter as a subordinate ingredient.
Dr. P. C. Sutherland, in 1853, describes the east coast of Baffin island between Lancaster sound and Cumberland gulf as follows:
‘On the opposite shore (south) of Lancaster sound, at Cape Walter Bathurst, the crystalline rocks are again recognized, and from this point they occupy the whole coast south to Cumberland strait and probably considerably beyond it. To this, however, I believe there is one exception, at Cape Durban, on the 67th parallel, where coal has been found by whalers; and also at Kingaite, two degrees to the southwest of Durban, where from the appearance of the land as viewed from a distance, trap may be said to occur on both sides of the inlet. Graphite is found abundant and pure in several islands situated on the 65th parallel of latitude, in Cumberland strait, and on the west side of Davis strait.’
C. F. Hall brought home a considerable collection of rocks and minerals picked up during his explorations about Frobisher bay and the southeast coast of Baffin island. These were named by Prof. B. K. Emerson, and consist of ordinary Laurentian rocks, including granite, gneiss and schists. The minerals were magnetite, apatite, bornite and pyrite from Frobisher and Cyrus Field bays. Lower Silurian limestones were found in a small outlier at Silliman’s Fossil Mount near the head of Frobisher bay. This locality was visited in 1897 by a party from the Peary Arctic expedition of that year. In the course of a few hours they obtained fifty-four species of fossils from this locality, which were later named by C. Schuchert.
Dr. Franz Boas describes the nucleus of the mountain masses of Baffin island to be everywhere gneiss and granite, with Silurian limestones about the region of the large lakes of the interior and along the low lands of the west coast.
Dr. R. Bell visited the north shores of Hudson strait in 1884 and 1885, and again in 1897, when he made a close examination of the coast from the neighbourhood of Big island to Chorkbak inlet near Gordon bay. Dr. Bell describes the prevailing rocks of the southern shore of Baffin island as consisting of well stratified hornblende and mica-gneiss, mostly gray in colour, but sometimes reddish, interstratified with great bands of crystalline limestones, parallel to one another and conformable to the strike of the gneiss, which in a general way may be said to be parallel to the coast in the above distance. The direction, however, varies somewhat in different sections of the coast.
‘The distinguishing feature in the geology of the southern part of Baffin land is the great abundance, thickness and regularity of the limestones associated with the gneisses. At least ten immense beds, as shown on the accompanying map, were recognized, and it is probable that the two others, discovered in North bay, are distinct from any of these. There would, therefore, appear to be twelve principal bands as far as known, to say nothing of numerous minor ones, between Icy cape and Chorkbak inlet. The limestones are for the most part nearly white, coarsely crystalline, and mixed with whitish feldspar.————The limestones usually contain scattered grains of graphite, and among the other minerals which commonly occur in the various bands are mica, garnet, magnetite, pyrite and hornblende.’
‘Although white is the prevailing colour of these limestones, this, in some localities, is replaced by light-gray and occasionally by mottled varieties.’
‘The limestone bands have not suffered greater denudation than the gneisses, and they form hill and dale alternately with the latter.————Owing to the scantiness of vegetation in Baffin land, the white colour of the limestones on the sides and tops of the hills and ridges renders them very conspicuous in the landscape. Seen from a hill-top at a distance of fifteen or twenty miles, they might be taken for glaciers.’
‘As to the total thickness of the twelve bands of crystalline limestone which have been mentioned as occurring in this part of Baffin land, the available data on the subject are not sufficient to form a correct estimate, but on adding together their probable approximate widths it seems to be no exaggeration to place their possible total volume, great as it may appear, at about 30,000 feet, or on an average of 2,500 feet for each of the principal bands, taking no account at all of the smaller ones.’
From his observations made along the coast to the eastward of Big island in 1885, and from the finding of crystalline limestone fragments by Hall in Frobisher bay, Dr. Bell concludes that the crystalline limestones extend eastward to Resolution island, giving a very extensive development of the Grenville series of the Laurentian in the southern part of Baffin island.
At present we know that the limestones of the typical Grenville series are only the highly crystalline equivalents of some of the Huronian limestones. This probably is the case in Baffin island, where these rocks with some of the accompanying gneisses represent a highly metamorphic phase of portions of the Huronian, while other of the gneisses are the foliated state of the granite masses which caused the alteration of the limestones. This would correlate the rocks on the north side of Hudson strait with the altered Huronian rocks of northern Labrador, where in places similar crystalline limestones occur.
Cape Haven Harbour.
The Huronian rocks of Labrador are marked by the number of repetitions of the strata caused by thrust faults in all the areas examined, and this repetition of measures by similar faults may account for the number of bands of limestone found in the southern part of Baffin island.
The crystalline rocks appear to form the southwest coast of Baffin island for some distance beyond King cape on the east side of Fox channel, when they give place to a wide area of low lands extending nearly to the head of Fox channel, where the crystalline rocks again form the higher lands to the north and east of Fury and Hecla strait.
On the late voyage of the Neptune the rocks of the east side of Baffin island were examined at Ponds inlet, on the islands on both sides of Cumberland gulf, and at Cape Haven and Frenchmans cove on Cyrus Field bay. In other places the ship passed sufficiently near the shores to allow of a good idea being formed of the rocks by the aid of powerful glasses.
Examinations of the rocks were made at Button point, the southeast part of Bylot island, on the north side of the entrance to Ponds inlet; also in the vicinity of Salmon river some thirty miles up the inlet and on its south side, and at Erik harbour on the same side near the mouth of the inlet. At all these places typical Laurentian gneisses and schists were obtained. Among the specimens brought home from these localities is a light-coloured coarse-grained augen-gneiss consisting largely of white and pink feldspar, with thin bands of biotite and little quartz. Another seeming variety of this rock is a well-banded fine-grained mica-gneiss composed of pink and white bands of feldspar separated by thin bands of mica. Associated with these are bands of very quartzose gneiss varying in colour from light to dark from the varying proportions of mica present. These gneisses are usually found containing a considerable number of dark-red garnets; and they probably represent a metamorphic series. A fine to medium-grained rock, usually somewhat foliated, and composed largely of dark-red feldspar with much mica, little hornblende and quartz, cuts the foregoing gneisses, and probably was the granite which altered them by intrusion to their present state. The basic intrusive rocks are represented by dark-green diabase, or its alteration products, dark hornblendic and chloritic schists and gneisses. Taken as a whole, this series of specimens would answer for any of the typical Laurentian regions of northern Canada.
At Cumberland gulf the rocks were examined at Kaxodluin on the south shore, some twenty miles from Blacklead station; also at Blacklead and at Kekerten islands. At Kaxodliun light and dark-coloured mica schists and gneisses were found, cut by a light-pink mica-granite-gneiss. The dark schistose rocks were decomposed near the surface, and contained a considerable amount of disseminated pyrite. Between this place and Blacklead the ship followed the shore-line closely, so that the prevailing dark, rusty gneisses were distinctly seen.
The most abundant rock on Blacklead island is a coarse-grained, pink mica-granite-gneiss, containing large feldspar crystals. This cuts, and is foliated with, coarse, dark mica-schists, and finer-grained lighter-coloured quartzose gneisses. Some of the dark schists contain flakes of graphite, and this mineral is said to be abundant in places on the islands and shores of the gulf farther to the westward, where attempts have been made to work some of the mica and graphite deposits, without much success.
At Kekerten similar gneisses are found, along with large masses of diabase and greenstone, somewhat decomposed near the surface, where it weathers reddish.
At Frenchman cove at the head of Cyrus Field bay, the prevailing rock is a coarse-grained, red mica-granite-gneiss, associated with bands of coarse mica-schist.
At Cape Haven station near the northern entrance to the bay, pink and gray mica-gneiss prevails, and is cut by many large dikes of red pegmatite composed largely of perthite, with some quartz and mica. Schists forming one of the islands of the harbour contain many well-developed crystals of pyrite, up to an inch cube.
The northern and eastern sides of Bylot island appear to be wholly formed of crystalline rocks, without any of the capping limestones found upon the other islands of Lancaster sound.