284 Dr. J. Croll on the Cause of 



its base to the Lower Bagshot Sand. It has, he says, been 

 intersected bj cuttings in all directions and at all horizons, 

 but has not yielded a trace of any thing indicating a cold and 

 glacial condition of things. The same, he adds, holds true of 

 the strata in France and Belgium. Further, u 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 Eocene, 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 geo- 

 logists 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 

 was, we need not wonder that no trace of glaciation so remote 

 as that of the Eocene period is now to be seen. Besides all 

 this, there is in the south of England the land-surface on 

 which the glaciation, if any, took place, whereas not a vestige 

 of the old land-surfaces of the Eocene period now remains. 

 It therefore seems to me that the mere fact of nothing as yet 

 having been found in the Tertiary deposits of the south of 

 England, indicating one or more cold periods, is no proof that 

 there may not possibly have been such periods, and even of 

 considerable severity. The same remarks hold equally true 

 in regard to the deposits on the continent referred to by 

 Mr. Wood. 



It will be urged in reply that there is one kind of evidence 

 which ought to be found, as it could not possibly have been 

 obliterated by the destruction of the Tertiary land-surfaces : 

 that is, the presence of erratic blocks and foreign rock- frag- 

 ments imbedded in the strata. Mr. Wallace states that in the 

 many thousand feet in thickness of alternate clays, sands, 

 marls, shales, and limestones no irregular blocks of foreign 

 material or boulders characteristic of glacial conditions are to 

 be found. The same, he says, holds equally true of the 

 extensive Tertiary deposits of temperate North America. 



If it be really the case that the Tertiary beds are wholly 

 without boulders or fragments of foreign material, then this 

 certainly may be regarded as proof that no real glacial epoch 

 could have occurred during that period. But has it been 



