The north shore of Bear Lake is low, and is skirted by many shoals, formed by boulders of limestone. No rocks, in situ, are exposed between Limestone Point and the Scented Grass Hill, a remarkable promontory, which separates Smith and Keith bays. Its height above the lake is betwixt eight and nine hundred feet, and in form and altitude it corresponds with the Great Bear Mountain, which, lying opposite to it, separates M'Vicar and Keith bays. I did not ascend either of these hills; but cliffs, corresponding in character to those of the aluminous shale-banks at Whitby, flank their bases; and the same formation probably extends along the north shore of Keith Bay, and some way down Bear Lake River. The ground skirting the Scented Grass and Great Bear Mountains is much broken, and consists of small, rounded and steep eminences, separated by narrow vallies and small lakes. Several shelving cliffs, about one hundred feet high, and some miles in extent are washed by Bear Lake. 251
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They consist of slate-clay and shale, more or less bituminous, and the dip of the strata is in several places to the N.W. by N. At the foot of the Scented Grass Hill a rivulet has made a section to the depth of one hundred feet, and here the shaly beds are interstratified with thin layers of blackish-brown, earthy-looking swinestone, containing selenite and pyrites. Globular concretions of the same stone, and of a poor clay iron-stone, also occur in beds in the shale. The surfaces of the slates were covered with an efflorescence of alum and sulphur. Many crystals of sulphate of iron lie at the bottom of the cliff, and several layers of plumose alum, half an inch thick, occur in the strata. At the base of Great Bear Mountain, the bituminous shale is interstratified with slate-clay, and I found imbedded in the former a single piece of brown coal, in which the fibrous structure of wood is apparent. Sections of slate-clay banks, and more rarely of bituminous shale, occur in several places on the north shore of Keith Bay. In one place, about seven or eight miles from Bear Lake River, a bed of plastic and bituminous clay occurs, and in another, near Fort Franklin, there is a deposit of an earthy coal, which possesses the characters of black chalk.
It is probable that a magnesian limestone underlies this formation of bituminous shale. I have already mentioned the beds of dolomite, which are exposed on the north side of Bear Lake, and similar beds occur to the southward of the Great Bear Mountain, forming cliffs on the shores of M'Vicar Bay. At Manito Point, on the west side of the isthmus that connects Great Bear Mountain to the main shore, a low ridge of limestone rocks terminates on the borders of the lake, forming some bold cliffs and a remarkable cave. The stone has a gray colour and bituminous smell, and contains much interspersed calc-spar. The strata dip to the north-west.
VICINITY OF FORT FRANKLIN, GREAT BEAR LAKE.
Fort Franklin stands on the northern shore of Keith Bay, about four miles from Bear Lake River, upon a small terrace, which is elevated twenty-five or thirty feet above the lake. The bay, contracting towards the river, is about four miles wide opposite to the fort, and the depth of water there does not exceed four fathoms. Farther from the river, the east and west shores of Keith Bay recede to the distance of thirty miles from each other, and the depth of water in the centre of the channel greatly increases. The bottom of this bay, wherever it could be distinguished, was observed to be sandy, and thickly strewed with round boulders[23] of various primitive rocks of large size, which were particularly abundant near the river, and with large square blocks of limestone, most plentiful near the cape formed by the Scented Grass Hill. In the small bay between the fort and the river, shoals are formed by accumulations of boulders, and the shores are thickly strewed with them. 261 to 308Many of these travelled blocks consist of flesh-red granite, having only a small quantity of black mica, exactly resembling the primitive rocks seen in M'Tavish Bay, but noticed no where else near the lake. Boulders of the same description occur in shoals at the mouth of M'Tavish Bay, and on the shores which skirt the Scented Grass Hill which faces that bay, to all which places they may have been brought from the parent rock, by a current flowing from the east. On the northern shore of Bear Lake the great majority of the boulders consists of limestone. 266 282Two varieties of granite, which occur amongst the boulders, were recognised as being abundant rocks at Fort Enterprise, which is situated about one hundred and seventy miles south-east from M'Tavish Bay. Some of the boulders were of a peculiar-looking porphyry exactly resembling that which occurs in the height of land betwixt the Coppermine River and Dease Bay; several of sandstone and conglomerate, which probably came from the same quarter; of greenstone, perhaps, from the Copper Mountains, and of limestone from the northern shores of the lake, and from the isthmus of the Great Bear Mountain; all these places lying to the eastward or north-east.
The soil in the immediate vicinity of Fort Franklin is sandy, or gravelly, and covers, to the depth of one or two feet, a bed of clay of unknown thickness. Gravel taken from a spot thirty feet above the present high-water level of the lake, and out of the reach of any stream or torrent, contained rounded pebbles of granite, of greenstone, of quartz rock, of lydian stone, and of various sandstones, of which some were spotted, and others presented zones of different colours. These sandstones form a considerable portion of the gravel.[24]
The clay which lies under the soil is of a bluish-gray colour, and is plastic but not very tenacious. It is more or less mixed with gravel. During the greater part of the year it is firmly frozen; the thaw in the two seasons we remained there never penetrating more than twenty-one inches from the surface of the earth. In spots where the sandy soil is wanting, the clay is covered a foot deep, or more, by mosses, mostly bryum palustre, and some marsh hypna and dicrana, in a living state, for they seem to be converted very slowly into peat in this climate.
The ground rises gradually behind the fort, until it attains, at the distance of half a mile from the lake, the height of two hundred feet, forming, when viewed from the southward, an even ridge, running nearly east and west—which ridge is, in fact, the high bank of the lake, as it corresponds in height with the summit level of the banks of Bear Lake River, and of the southern shore of Keith Bay. The country extending to the northward, from the top of the bank, is nearly level, or has a very gentle ascent for about five miles, when a more abrupt ridge rises to perhaps three hundred or four hundred feet above the lake. The view from the summit of this second eminence is very extensive, the whole country as far as the eye can reach appearing to be a level, from which several narrow precipitous ridges of limestone arise. But, although the country around these ridges appears from a distance to be level, or very slightly undulated, yet it abounds in small eminences and steep-sided vallies of various shapes, some being rounded and basin-shaped, others long and narrow. Lakes and swamps are here so numerous, that the country, for at least sixty miles to the northward, is impassable in summer, even to the natives. There are many mounds of sand and gravel, and fragments of sandstone are frequent; but having travelled in this direction only in winter, when the ground was covered to the depth of upwards of three feet with snow, I had not an opportunity of examining its geological structure. White spruces cover the drier spots; larches, black spruces, and willows abound in moist places; the sandy hillocks are clothed with aspens, and the sides of the vallies support some canoe birches, with a thick undergrowth of dwarf birches, alders, and rose-bushes. The eminence from whence the view just described was obtained, appears like a ridge only in approaching it from the lake, for it rises very little above the general level of the country behind it. It has a direction from N.W. by N. to S.E. by S., and terminates about eight miles to the eastward of the fort, in a small bluff point on the shores of the lake and there the strata consist of slate-clay slightly bituminous. The banks immediately behind the fort also exhibit, in their ravines, a bluish slate-clay.
The land on the south side, or bottom, of Keith Bay, presents a nearly similar aspect to that just described, rising, on the borders of the lake, to the height of one hundred and fifty feet, and then running back to a great distance nearly level. It may be characterized as full of hollows, narrow vallies, ravines, and lakes; but it is not hilly, although it is traversed by ridges of limestone, which rise like walls through the flat country. The nearest of these ridges terminates on the borders of the lake at the Manito Point, (noticed in page vii.) It may be proper to remark here, that, in addition to the limestone ridges visible from Fort Franklin, or from the heights behind it, the summit of Clark Hill, bearing south, and forming part of a ridge about fifty miles distant, was distinctly seen. This hill lies behind Old Fort Norman on the Mackenzie, and has more the outline of a granitic rock, although some of the peaks which skirt it have the serrated crests which the limestone ridges in this quarter show. It was guessed to be 1500 feet high above the Mackenzie.
This sketch of the general features of the country about Fort Franklin being premised, the ensuing geological notices follow in the order of the route of the Expedition.