Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/945

 streams, — these green grassy valleys being then beds of glaciers ; and the gloomy glens scattered with boulders, deep fjords, through which icebergs sailed to the open sea. I consider that the greater portion of the Loess, or Lehm, of the Alpine valleys, and even of France, is due to the same cause (viz. the deposit from the glacier-rivers), and that, in fact, it is identical in character with the laminated fossiliferous glacial clays. It differs from them, however, in this respect, that this clay was spread over alpine valleys without so much assisting power from water as if the rivers had fallen into the sea, was not disturbed by boulders scattered through it, or icebergs ploughing it, but that the land shells found in it are theoretically of the same nature as the marine shells found in the glacial clays, viz. the fauna of the overspread region ; much of the loess, however, was doubtless due to the present great continental rivers. In many places (as in Caithness) we only find the upper fossiliferous clay without the under " till ; " and in this case I consider that the clay was deposited before a surface with moraine profonde was exposed ; for be it noted that it was only as the glaciers were clearing off, either by increased heat, or by breaking off in bergs when the country got sunk to the depth mentioned (more or less, it does not matter), that the two clays were formed one above another in the manner described ; for only then could the moraine profonde, or " till," get exposed for the upper laminated clays to form above it 1.

3. Kaimes, Escars, Oscars, or Gravel Mounds, &c. — The glacial clays often contain nests of gravel, and beds of sand interstratifying with the clays. How these were formed can be easily understood by any one who has seen the icefoot and the icebergs scattering their gravel and stones over the bottom ; and how certain districts should have gravels and others clay is, in my opinion, equally apparent, because, if the theory enunciated in this paper be correct, then the fossiliferous Boulder-clay could only be limited to certain districts, as in Davis Straits at the present day. The curious ridges of gravel &c. variously designated by the names at the head of this section are, I am strongly inclined to believe, merely the sand- and gravel- banks of the old glacial sea, and are very nearly equivalent to what the present " cod-banks" (Rifkol &c.) in Davis Straits would be if the bed of that sea were laid bare. Against this theory, however, there stands the fact that hitherto no marine remains have been got in these " Kaimes " (as they are called in Scotland, " Eskars " in

1 Since this was written, a most interesting and suggestive paper has been published by Mr. James Croll " On the Boulder-clay of Caithness as a product of land-ice" (Geol. Mag. vol. vii. pp. 209-214, and pp. 271-278), in which he endeavours, with much plausibility, to prove that this clay is part of the bed of the North Atlantic pushed forward by a huge glacier, which at that time, he considers, filled up the greater part of that sea, the ice from Scandinavia being, he considers, too thick to float in the comparative shallow sea into which it must have protruded either in the form of icebergs or of glaciers. Without giving my adherence to a theory so sweeping, I cannot but admire the logical manner in which Mr. Croll reasons out his hypothesis, and the interest and importance of his suggestion— much too important, indeed, to be discussed in the foot-note with which I must at present dismiss it.

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