Date of the Glacial and the Upper Miocene Period. 367 



glacial epoch, a conclusion which we know from geological evi- 

 dence is incorrect. Influenced by these considerations, I ex- 

 pressed the opinion that it might yet turn out that between 

 240,000 and 80,000 years ago was the period of the glacial 

 epoch, and that that epoch of glaciation about 850,000 years 

 ago might be that of the Upper Miocene period. 



There are physical reasons of great weight against the opinion 

 that the glacial epoch was so remote as 850,000 years ago. If 

 we place the middle of the glacial epoch 850,000 years back, then 

 we must lengthen out to a corresponding extent the entire geo- 

 logical history of our globe. Sir Charles Lyell considers that 

 when we go back as far as the Lower Miocene formations, we 

 arrive at a period when the marine shells differed as a whole 

 from those now existing. But only 5 per cent, of the shells ex- 

 isting at the commencement of the glacial epoch have since died 

 out v Hence, assuming the rate at which the species change to 

 be uniform, it follows that the Lower Miocene period must be 

 twenty times as remote as the commencement of the glacial 

 epoch. Consequently, if it be 1 million of years since the com- 

 mencement of the glacial epoch, 20 millions of years, Sir Charles 

 concludes, must have elapsed since the time of the Lower Mio- 

 cene period, and 60 millions of years since the begininng of the 

 Eocene period, and about 160 millions of years since the Carboni- 

 ferous period, and about 240 millions of years must be the time 

 which has elapsed since the beginning of the Cambrian period. 

 But, on the other hand, if we refer the glacial epoch to the later 

 period of great excentricity, and take 250,000 years ago as the 

 beginning of that period, then, according to the same mode of 

 calculation, we have 15 millions of years since the beginning of 

 the Eocene period, and 40 millions of years since the Carbonife- 

 rous period, and 60 millions of years in all since the beginning 

 of the Cambrian period. 



A great many considerations seem to show that 850,000 years 

 cannot possibly have elapsed since the glacial epoch, and that we 

 must assign that epoch to the period commencing about 240,000 

 years ago and extending down to about 80,000 years ago. If 

 the glacial epoch be placed at so remote a period as 850,000 years 

 ago, then it is very probable, as Sir Charles Lyell concludes, that 

 the beginning of the Cambrian period will require to be placed 

 240 millions of years back. But we have evidence of a phy- 

 sical nature which proves that it is absolutely impossible that the 

 existing order of things, as regards our globe, can date so far back 

 as anything like 240 millions of years. The arguments to which 

 I refer are those which have been advanced by Professor Sir Wil- 

 liam Thomson at various times. ■ These arguments are well 

 known, and to all who have really given due attention to them 



