Читать книгу Arctic Searching Expedition (Sir John Richardson) - comprehensive & illustrated - (Literary Thoughts Edition) онлайн

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On the summit of the canoe-route between Lakes Superior and Winipeg, a sheet of water, bearing the analogous appellation of Thousand Lakes, is also studded with knolls of granite, forming islets; but low mural precipices are more common there; and there is, moreover, an inter-mixture of accumulations of sand, such as are commonly found on the summit of the water-shed, along its whole range. The general scenery of this lake is similar to that of the Thousand Islands; but though the elevation above the sea does not exceed fourteen hundred feet, the voyagers say that frosts occur on its shores almost every morning throughout the summer.

Silurian strata occur on both flanks of both arms of the water-shed above spoken of, to a greater or smaller extent throughout their whole length. When we descend to Lake Winipeg we come upon epidotic slates, conglomerates, sandstones, and trap rocks, similar to those which occur on the northern acclivity of the Lake Superior basin; and after passing the straits of Lake Winipeg, we have the granite rocks on the east shore, and silurian rocks (chiefly bird's-eye limestone) on the west and north, the basin of the lake being mostly excavated in the limestone. The two formations approach nearest to each other at the straits in question, where the limestone, sandstone, epidotic slates, green quartz-rock, greenstone, gneiss, and granite, occur in the close neighbourhood of each other.