Date of the Glacial and the Upper Miocene Period. 363 



Let it be observed that it is not essential to the object in view 

 to be able to show from the facts of geology that former cold pe- 

 riods, such as those of the Eocene and the Miocene, were as severe 

 as that of the glacial epoch. All that is required is simply to show 

 that, for anything that geology can prove to the contrary, those 

 cold periods may have been as severe as the glacial epoch. What 

 I wish to show is, that although the conclusions derived from 

 astronomical and physical considerations regarding the severity 

 of former ice-periods may not at present be fully borne out by 

 geological science, the imperfection of geological records upon 

 this point is such that the absence of direct geological evidence 

 cannot reasonably be regarded as sufficient proof that the phy- 

 sical conclusions arrived at are improbable. But this is not all ; 

 I shall endeavour to show that the records of geology in regard 

 to former glacial epochs are not only imperfect, but that this 

 imperfection follows as a necessary consequence from the principles 

 of geology itself — that there is not simply a want of records, but 

 a reason in the very nature of geological evidence why there is 

 such a want. 



Geological evidence in reference to past glacial epochs is evi- 

 dently much more imperfect than many suppose. 



It is on a land-surface that the principal traces of the action 

 of ice during a glacial epoch are left ; for it is there that the 

 stones are chiefly striated, the rocks ground down, and the 

 boulder-clay formed. But where are all our ancient land-sur- 

 faces ? They are not to be found. The total thickness of the 

 stratified rocks of Great Britain, according to Professor Ramsay, 

 is nearly fourteen miles. But from the top to the bottom of this 

 enormous deposit there is hardly a single land-surface to be found. 

 True, there are patches of old land- surfaces of a local character, 

 such, for example, as the dirt-beds of Portland ; but, with the ex- 

 ception of the coal-beds, every general formation from top to 

 bottom was formed under water, and none but the under-clays 

 ever existed as a land-surface. And it is here in such a forma- 

 tion that the geologist has to collect all his information regard- 

 ing the existence of former glacial epochs. The entire strati- 

 fied rocks of the globe, with the exception of the coal-beds and 

 under-clays (places where no one would expect to find traces 

 of ice-action), consist almost entirely of a series of old sea-bottoms, 

 with here and there an occasional freshwater deposit. Bearing 

 this in mind, what is the sort of evidence which we can now 

 hope to find in these old sea-bottoms of the existence of former 

 ice-periods ? 



Every one, of course, who has ever reflected on the matter ad- 

 mits that the stratified rocks are not old land-surfaces, but a 

 series of old sea-bottoms formed out of the destruction of old 



