Page:Quarterly Journal of the Geological Society of London, vol. 29.djvu/33

 brief geological account of the mining-districts of Thunder Bay and Shabeudowan, both of which are likely to become ultimately of great importance. Though as yet very imperfectly explored, and still more imperfectly opened up and developed, the entire north shore of Lake Superior has already been shown to be intersected by numerous metalliferous veins, and promises to equal in richness the most celebrated mining-regions of the North American continent. At present, however, I shall confine my attention to the silver-bearing district of Thunder Bay, and the auriferous region which surrounds Lake Shabendowan.

Thunder Bay, Black Bay, and Neepigon Bay are three remarkable bays on the north shore of Lake Superior, almost shut off from the main lake by islands, and assuming more or less the character of independent lakes. The first of these is the most westerly, and is a beautiful sheet of water, about 28 miles in length and 12 miles across. On its northern shore are situated the settlements of Port William and Prince Arthur's Landing, the former a Hudson's Bay port of comparative antiquity, the latter a newly established town, destined to be the centre of the silver-mining district. The chief river flowing into Thunder Bay is the Kaministiquia, a large and important stream, which drains a series of lakes lying to the north of Lake Superior, and which debouches into the latter at Port William. The bay, as viewed from its northern shore, appears to be almost land-locked, and presents several features of striking interest, both from a geological and an artistic point of view. Facing Prince Arthur's Landing, to the south-east is the bold and bare prominence known as Thunder Cape, which is 1350 feet above the level of the lake, and more than 2000 feet above the level of the sea. The lower portion of this rugged elevation is formed of black argillaceous shales, whilst the higher portion is constituted by a vast tabular mass of columnar trap interstratified with the former. Both of these belong to what Canadian geologists term the " Copper- bearing Series," of which I shall have to speak again. The mouth of Thunder Bay is divided into two channels by several islands, the largest of which is Pie Island, which derives its somewhat unromantic name from the presence on its western end of a great rounded, flat-topped, pie-shaped mass of trap, forming a continuation of the great overflow of Thunder Cape. To the west, again, on the mainland, and beyond the mouth of the Kaministiquia river, the same trap is continued into a great series of rugged hills, of which the one known as " Mackay's Mountain " has an elevation of 800 feet above the level of Lake Superior.

The rocks which immediately surround Thunder Bay belong to the so-called "Lower" and "Upper Copper-bearing Series" of Canadian geologists. The relations which subsist between these two groups have not yet been satisfactorily determined ; and the age of both is still a matter of opinion. The Upper Copper-bearing series consists essentially of red, white, and grey dolomitic sandstones, red sandstones and shales, reddish limestones, indurated red and yellowish marls, red sandstones and conglomerates, and inter-

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