The Laurentian System Around Hudson’s Bay.

Nucleus of the continent.

Basin of Hudson’s Bay.

Palæozoic strata.

Fox Channel.

The vast Laurentian area of the north-eastern part of North America forms a very considerable proportion of the whole continent and, geologically speaking, it may be regarded as its nucleus. Greenland, on the other side of Baffins’ Bay and Davis’ Straits, consists, as far as known, almost altogether of the same rocks. Hudson’s Bay, which is nearly half as extensive as the Mediterranean Sea, lies in the middle of the continental portion of the great Laurentian area and the waters drain into it from all sides. The country slopes towards it from the Rocky Mountains, more than 1,300 miles to the westward, from the centre of Labrador, 500 miles to the eastward and from the immediate vicinity of Lake Superior in the south. Thus, the waters of this great interior sea occupy only the centre of what may be called the basin of Hudson’s Bay. This wide depression has existed from early geological times, as is shown by the Manitounuck rocks of the eastern shore and islands and by the Silurian limestones of Mansfield and Southampton Islands and of the southwestern shores of Hudson’s Bay and James’ Bay, as well as the Devonian rocks of the latter. These flat-lying palæozoic strata probably also extend over much of the bed of the bay, judging by its shallowness and the uniform depth of its waters, and also from the composition of the materials of the drift which have been carried out of it during the glacial period. None of the unaltered rocks around the Bay have undergone any marked disturbance, so far as known. The observations of Dr. Franz Boas and others around Fox Channel would lead us to suppose that from a geological standpoint this body of water is a repetition of Hudson’s Bay on a smaller scale (see above).

Source of volcanic rocks.

Clearwater Lake.

The Manitounuck series is largely made up of rocks of volcanic origin and I have obtained specimens of diorites and porphyry from the north-western part of the bay. The probable site of the original source from which these rocks have been derived has not yet been ascertained. A set of immense dykes of trap along the Mattagami River running northward towards James’ Bay, was described in my report for 1875; and other dykes, having the same general course, were found along the east side of James’ Bay in 1877. No irregularity has been found in the bottom of Hudson’s Bay which might indicate a seat of volcanic disturbance in former times. The unexplored district behind Cape Henrietta Maria may yet throw some light on this subject. The volcanic rocks of the Manitounuck group of the Eastmain coast and the islands opposite to it may have been originally derived from the neighbourhood of Clearwater Lake to the eastward of Richmond Gulf. Between Lake Superior and Hudson’s Bay, I have observed that, other things being equal, the water of lakes where igneous rocks prevail, is much clearer than those surrounded by gneiss or schists. The Rev. Mr. Peck visited the lake referred to in 1884, and he informs me that it merits its name from the clearness of its waters.

Schistose bands.

Labrador Peninsula.

Schistose bands and areas which have been classified as Huronian are largely developed within the general limits of the Laurentian country to the south and west of James’ Bay and apparently also on the north-west side of Hudson’s Bay, but to the eastward few indications of these rocks have yet been discovered. The Labrador peninsula measures, as nearly as possible, 1,000 miles from the Straits of Belle Isle due west to the Eastmain coast of James’ Bay, by 1,000 miles from Cape Wolstenholme, on Hudson’s Straits, to Mingan on the Gulf of St. Lawrence. The interior of this vast region has not yet been explored geologically, except to a very limited extent, so that rocks of the class called Huronian may exist in great force in some parts of it. A non-fossiliferous, but unaltered limestone, like those of the Manitounuck group is found around Lake Mistassini near the head of the Rupert River in the southern part of the above region.

Rocks of Baffin Land.

The gneissic rocks of the east coast of Hudson’s Bay have been described in my reports for 1875 and 1877, and those of Hudson’s Straits in the report for 1884. Dr. Frans Boas, in the course of his explorations has made some notes on the fundamental rocks of Baffin Land, which stretches from Hudson’s Straits northward through twelve degrees of latitude, or to Lancaster Sound. At page 57 of his report (Dr. A. Petermann’s Mitteilungen aus Justus Perthes Geographischer Anstalt, Nr. 80. Gotha. Nov. 1885), he says: “Let us, in conclusion, cast a glance on the geological structure of the last mentioned territory (the northern part of Baffin Land). The nucleus of the mountain masses appears to be everywhere gneiss, which I found especially at Kinguait and Panguirtung. In closest combination with the gneiss, granite, also occurs, which, especially large-grained, appears in the coast ranges and islands.—Anarmtung and Nuvakdjuak in Cumberland Sound; Padloping, Kexertaxdjuin, Nudlung, Tupirbikdjawitjung and Siorartijung on Davis Strait.”

Cumberland Sound.

“In Cumberland Sound, as well as in the Naguimiut plateau, which latter is mostly composed of fine-grained granites, there are found at isolated places, diorites and trap-granulites which have broken through the granite. The occurrence of these to the south on Blunt peninsula, has been confirmed. In Cumberland Sound I found them at Panguirtung and in a well-marked dyke in Akuliaxling eastward from Kexerten. The same diorite appears also in the mountain Kaliugujang to the east of Kinguait.”

Rocks of other northern localities.

“The Silurian limestones, overlying the old crystalline rocks, have been already mentioned. The same are found besides in Field Bay, and they compose nearly the whole northern coast of Baffin Land. Hall found sandstone at Lock’s Land, which perhaps belongs to the Carboniferous formation. It is said to resemble that found by Parry at Antridge Bay (Fury and Hecla Strait). Here may also be mentioned the samples of sandstone found by Bessils at Point Garry. From accounts by Captain Walker of the ship “Erik,” coal is found in loose boulders in a stream at Eclipse Sound and on Aggidjeu (Durban Island).”

Characters of gneisses.

Useful minerals.

The gneissic rocks within the immense area which has been described, no doubt represent a great period of geological time, and comprise a vast thickness of strata, the amount of which it would be impossible to determine with any degree of accuracy. Certain areas of a massive granitoid character, are regarded as “primitive” gneiss, and there is little doubt they are more ancient than those Laurentian rocks which are regularly and distinctly stratified, and consist of bands of different lithological characters, such as prevail in the Ottawa valley. As a general rule, in the great region around Hudson’s Bay, the gneiss is of a very monotimous character, consisting of the commoner reddish and greyish varieties. It is mostly massive, highly crystalline and hard, except where it has been exposed for ages to atmospheric influences, as in the non-glaciated districts. The fresh rock will break almost as easily across the lines of stratification as parallel with them. The average direction of the lamination is sometimes pretty constant over a considerable extent of country, but it is as frequently, greatly contorted on the small scale, and so much disturbed on the large scale as to render it almost impossible to trace out and map its structure. The gneisses of this kind are not known to carry any useful minerals, except such as mica and felspar in coarse granite veins. On the other hand, in the more southern districts, where the gneisses are somewhat regular, and where their different divisions are capable of being mapped, we find phosphate of lime, graphite, limestone, barytes, serpentine, magnetite and hematite, pyrites, galena, copper ores, &c. These rocks appear to be newer than the massive gneisses which prevail in the north.

Evidences of relationship in age.

The continuity and the geographical compactness of the great metamorphic or Laurentian area of the north-eastern part of the continent are themselves evidences of the close relationship in age of the rocks comprised within it, whereas there is more room for uncertainty on this point in reference to widely separated areas of metamorphic rocks more or less surrounded by newer formations. The various bands of rock which in Canada have been recognized under the name Huronian all lie within the general geographical limits of the Laurentian country, and are either stratigraphically incorporated amongst the members of the Laurentian series, or present no want of conformity to them. A variety of altered rocks, bearing a strong resemblance to those of some of the Huronian bands are found elsewhere, as in the Eastern Townships and New Brunswick, but their relations to the Laurentian system cannot be so easily determined.

Quartzites of Lake Huron.

Associated rocks.

Useful minerals in Huronian rocks.

Geographical distribution of Huronian rocks.

The series of rocks on the north side of Lake Huron, to which the name Huronian was first applied, is made up largely of quartzites, but to the north and west of this region these form only a minor portion, or are altogether wanting in the bands called Huronian, and which are composed principally of the other rocks, associated with the Lake Huron quartzites. They consist of more or less massive diorites, argillaceous and dioritic slate-conglomerates, granites and syenites, schistose and jaspery iron ores, limestones or dolomites, and imperfect gneisses, together with a great variety of schists, such as mica and hydro-mica, talcoid, chloritic, dioritic, argillaceous, silicious, epidotic, hornblendic, felsitic and dolomitic. Within the general limits of the Laurentian area, nearly all the metallic ores and other useful minerals, as yet known, have been found in these rocks, and, therefore, their discovery and correct delineation on the geological map are important. As far as our explorations have gone, rocks of these kinds, and which may for convenience be styled Huronian, are much more abundant in the region between the Great Lakes and Hudson’s Bay than anywhere in the Labrador peninsula or north of Hudson’s Strait. They have been found at three places on the east coast of James’ and Hudson’s Bay. (See Report of 1877.) Mr. John McLean mentions them south of Ungava Bay. Some of the rocks of Nachvak, on the Atlantic coast, may be classified with them; and they are believed to occur at Ramah and near the entrance of Hamilton Inlet, on the same coast.