Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/944

 evident from what I have said ; indeed it is only necessary to get an explanation of the great body of appearances presented by the glacial remains in Scotland to turn the first part of this memoir to this end, and give the description of glacial action in Green- land as an explanation. These explanations I will shortly summarize : —

The glacial clays have received various subdivisions, each geologist subdividing them as best suited the particular theory he was advocating; but the broad one generally adopted is into (1) an under non-fossiliferous one, not due to the action of water, and (2) an upper or fossiliferous one due to marine agency. It is too much the custom among the numerous writers on the ' Glacial Period,' to describe one small locality or district with which they are familiar, and therefrom to deduce the explanation of a phenomenon which must have extended over immense regions. This is most misleading. We must first endeavour to explain the broad features common to every district, and then see if local deviations cannot be explained by mere local peculiarities.

1. The sub-Azoic Boulder-clay. — This I consider, with Agassiz, Jamieson, and other authors, not due to the agency of icebergs or marine ice, but as the moraine profonde, or the great ice-covering of this country when Britain lay under conditions such as now prevail in Greenland.

2. The Fossiliferous, Laminated or Brick-clays. — These I consider are due almost solely to the sub-glacier rivers depositing at the bottom of the sea clay in which mollusca burrowed. This clay was deposited above the "till" when the country sank to the extent of about 500 feet beneath the sea ; for beyond that height, in Scotland at least, we have no remains of marine shells. Part of it, I will not deny, may be due to the sea assorting portions of the previous non-fossiliferous till ; but that the greater portion of these clays are due to the causes mentioned, from what we see in Greenland I have no doubt. When the fossiliferous Boulder-clay lies directly on the bottom, then we may suppose that during the time the non-fossiliferous clay was forming on land under the glacier the sub-glacier rivers were depositing this mud in the sea. If it is not fossiliferous, then we must conclude either that the old fauna of the Tertiary period had left the sea, and that the arctic one had not taken possession of it, or that this absence of life was due to one or other of the causes I mentioned in sec. 6, p. 688, as causing the clay at present forming in the Greenland fjords to be azoic. Mr. Jamieson, indeed, considers that the fossiliferous clay might have been contemporary with the non-fossiliferous clay underlying it, and that the fauna found in it was really the fauna of the period. If this is true (and I am inclined to believe it), then, unless on the most natural supposition that the one was forming independently from the sub- glacial rivers of the ice cap which was forming the other, I do not see how, on his theory, the one could overlie the other. This fossiliferous clay is, curiously, generally found near the coast, and in localities which, in the glacial epoch, would be the outlets of glacier