144 = S. Croll—Cause of Mild Polar Climates. 
base to the Lower Bagshot Sand. It has, he says, been inter- 
sected by cuttings in all directions and at all horizons, but 
has not yielded a trace of any thing indicating a cold an 
glacial condition of things. The same, he adds, holds true of 
the strata in France and Belgium. Further, “the Oligocene 
of Northern Germany and Belgium, and the Miocene of those 
countries and of France, have also afforded a rich molluscan 
fauna, which, like that of the Hocene, has as yet presented no 
indication of the intrusion of any thing to interfere with its 
uniformly subtropical character.” 
In reply to all this it may be stated that the simple absence 
of any trace of glaciation in the Tertiary deposits of the South 
of England certainly cannot be regarded as conclusive 
against the existence of an epoch of glaciation during that 
period. Not many years ago geologists denied that there 
was any evidence to be found of glaciation in the South of 
England, and at the present time there are hundreds of geol- 
ogists who will not admit that that part was ever overridden 
by land-ice. If it is so difficult to find in that quarter 
evidence of the last glacial epoch, severe as that glacial epoch 
ments imbedded in the strata. Mr. Wallace states that in the 
many thousand feet in thickness of alternate clays, sands, 
maris, shales, and limestones no irregular blocks of foreig® 
material or bowlders characteristic of glacial conditions are t0 
u The same, he says, holds equally true of the exten- 
sive Tertiary deposits of temperate North America. 
If it be really the case that the Tertiary beds are wholly 
. 
without bowlders or fragments of foreign material, then this _ 
