Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/387

 difficulties without any necessity. A continuous lake must therefore be supposed to have existed among the present vallies of the Roy, the Spean, the Gloy, and Loch Lochy, independently of that portion of Strathspey which I have described above. This last connection we may for the present neglect, as well as those collateral bays or masses of water connected with the principal lake, which if restored, would also now flow to the sea. I have however so far conjectured their extent, by a glance over the surrounding country, as to have ventured on a map of them, so as to give a notion of the probable quantity and extent of water which must, under these supposed circumstances, have occupied this part of the country.

A considerable portion of Glen Lochy must therefore have formed a part of this common lake, and although we may not be able to determine its boundary in this direction, it must have extended at least to the north of the opening of Glen Gloy. But that valley opens nearly opposite to the middle of the present lake. Examining therefore its condition, we find that it is diminishing, in consequence of the increase of alluvial matter from the wasting action of the surrounding streams. As the same action of these streams must have produced the same effects in distant times, and as the permanence of the lines proves that the hills themselves have undergone no violent changes, the ground that includes Loch Lochy must always have been in a state of increase, not of waste, and the barrier to the north, is consequently beyond the limits of this lake. If now, we proceed northward through the great Caledonian valley, and attempt to discover the place of this supposed barrier, we get entangled in a series of similar difficulties, nor is it possible to fix on