COPPER MOUNTAINS.
The Copper Mountains rise perhaps eight or nine hundred feet above the bed of the river, and at a distance, present a somewhat soft outline, but on a nearer view they appear to be composed of ridges which have a direction from W.N.W. to E.S.E. Many of the ridges have precipitous sides, and their summits, which are uneven and stony, do not rise more than two hundred, or two hundred and fifty feet above the vallies, which are generally swampy and full of small lakes. The only rocks noticed when we crossed these hills on the late journey, were clay-slate, greenstone, and dark red sandstone, sometimes containing white calcareous concretions, resembling an amygdaloidal rock. On our first journey down the Coppermine River, we visited a valley where the Indians had been accustomed to look for native copper, and we found there many loose fragments of a trap rock, containing native copper, green malachite, copper glance, and iron-shot copper green; also trap containing greenish-gray prehnite with disseminated native copper, which, in some specimens was crystallized in rhomboidal dodecahedrons. Tabular fragments of prehnite, associated with calc-spar and native copper, were also picked up, evidently portions of a vein, but we did not discover the vein in its original repository. The trap-rock, whose fragments strewed the valley, consists of felspar, deeply coloured by hornblende. A few clumps of white spruce trees occur in the vallies of the Copper Mountains, but the country is in general naked. The Coppermine River makes a remarkable bend round the end of these hills.
After quitting the Copper Mountains, and passing a valley occupied by a chain of small lakes in lat. 67° 10', long. 116° 45', we travelled over a formation whose prevailing rocks are spotted sandstone and conglomerate, and which forms the height of land betwixt Bear Lake and the Coppermine River. The ascent to this height from the eastward is gradual, but the descent towards Bear Lake is more rapid. The country is broken and hilly, though the height of the hills above the sea is perhaps inferior to that of the Copper Mountains. The vallies through which the small streams that water the country flow, are narrow and deep, resembling ravines, and their sides are clayey. The ground is strewed with gravel.
The sandstone has very generally a purplish colour, with gray spots of various magnitudes. It is fine grained, hard, has a somewhat vitreous lustre and contains little or no disseminated mica.
The conglomerate consists of oval pebbles of white quartz, sometimes of very considerable magnitude, imbedded in an iron-shot cement. Many of the pebbles appear as if they had been broken and firmly re-united again. The conglomerate passes into a coarse sandstone.
Porphyry and granite form hills amongst the sandstone strata.
The porphyry has a compact basis, like hornstone, of a dull brown colour, which contains imbedded crystals of felspar and quartz, and occasionally of augite. It forms some dome-shaped and short conical hills.
The granite is disposed in oblong ridges, with small mural precipices. It has, generally, a flesh-red colour, and contains some specks of augite, but little or no mica. The granite and porphyry were observed only on the east side of the height of land, the brow of which, and its whole western declivity, is formed of sandstone. Boulders of granite and porphyry, precisely similar to the varieties which occur in situ on the height of land, are common on the beach at Fort Franklin, and on the banks of the Mackenzie above Bear Lake.
To the westward of the height of land, the country on the banks of Dease River is more level, and few rocks in situ were seen, until within five or six miles of Bear Lake, where the stream flows through a chasm, whose sides are composed of a soft, fine-grained red sandstone, like that which occurs in the vale of Dumfries, in Scotland. Several ravines here have their sides composed of fine sand, inclosing fragments of soft sandstone.
About three miles from the mouth of Dease River we came to a limestone formation, which has been already noticed in the account of the geological structure of the shores of Great Bear Lake.