14 O/i Drift. 



site, the whole mass of detrital matter, too, being very small, and 

 principally referable to merely local causes. 



I cannot quit this part of our subject without reminding you of 

 the lucid manner in which the authors of the ' Geology of Rus- 

 sia' have pointed out how well the above state of Northern Asia, 

 accords with the supposed existence of Mammoths during the gla- 

 cial epoch, and how happily Sir Charles Lyell and Professor Owen 

 explained the capabilities of those animals to sustain the hardships 

 of a cold climate. But before the publication of Dove's Map of 

 Isothermal Lines, we had no adequate means of accurately esti- 

 mating the effect of such conditions as those above assumed on the 

 climate of North-western Asia. The extension of the Atlantic 

 Ocean nearly to the foot of the Ural chain would heighten consi- 

 derably the mean annual temperature of the neighbouring land, 

 especially if the height of that chain was lower than at present, as 

 Sir R. Murchison supposes it to have been at the period in ques- 

 tion. But the great effect would consist in the lessening of the 

 enormous existing difference between the summer and winter tem- 

 peratures already alluded to. The winter temperature would, doubt- 

 less, be very much moderated : and, therefore, any difficulty of 

 conceiving how great Pachyderms could exist through a Siberian 

 winter is in a great degree removed. Again, a much more ade- 

 quate reason is thus assigned for their subsequent disappearance 

 from that region. The cause to which this fact has been attri- 

 buted, is an increase of cold, arising from some additional elevation 

 of the Ural chain, and a rise of the region in general to the amount 

 of a few hundred feet. I believe it, however, to be certain that 

 these causes alone could produce but little influence on the cli^ 

 mate ; but, if we unite with them the withdrawal of the ocean 

 from the Ural chain within its present limits, we have an adequate 

 cause for changing the climate from one much more equable than 

 at present to the extreme of a continental one ; from a climate in 

 which the mammoth might exist, to one in which its existence dur- 

 ing the winter would be no longer possible. This would seem to 

 afford a very adequate cause for the disappearance of the mam- 

 moths from the Siberian region ; why they should not still have 

 sought a refuge in lands somewhat more southerly, which must 

 still have been open to them, may be a question of more difficult 

 solution. 



With respect to the order of events connected with the glacial 

 epoch, conclusions have sometimes been drawn which do not ap- 

 pear to me altogether warranted by the observed phenomena. The 

 striated and polished rocks, as fixed rocks in situ, must necessarily 

 be subjacent, where they exist, to the lowest beds of the drift, fre- 

 quently consisting of fine argillaceous and arenaceous matter. It 

 has been hence inferred that the process of striating and polishing 

 these subjacent rocks must have been altogether anterior to the 



