694 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 22, 
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 sum- 
marize :— 
The glacial clays have received various subdivisions, each geologist 
subdividing them as best suited the particular theory he was adyo- 
cating; 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-Azotc 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 ex- 
tent 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 Green- 
land 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. Jamie- 
son, indeed, considers that the fossiliferous clay might have been con- 
temporary with the non-fossiliferous clay underlying it, and that the 
fiuna 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 fossi- 
liferous clay is, curiously, generally found near the coast, and in 
localities which, in the glacial epoch, would be the outlets of glacier 
