XXXVl PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



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 question. But the great effect would 

 consist in the lessening of the enormous existing difference between 

 the summer and winter temperatures already alluded to. The winter 

 temperature would doubtless 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 

 adequate reason is thus assigned for their subsequent disappearance 

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

 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 climate ; 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 during the winter would be no 

 longer possible. This would seem to afford a very adequate cause 

 for the disappearance of the mammoths 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 appear 

 to me altogether warranted by the observed phsenomena. The stri- 

 ated and polished rocks, as fixed rocks in situ, must necessarily be 

 subjacent, where they exist, to the lowest beds of the drift, frequently 

 consisting of fine argillaceous and arenaceous matter. It has been 

 hence inferred that the process of striating and polishing these sub- 

 jacent rocks must have been altogether anterior to the whole process 

 of deposition of the finer matter, each of these processes occupying 

 distinct and separate intervals of time. No one would, of course, 

 suppose that the matter reposing on a given surface of striated rock 

 could have been deposited there before that surface became striated ; 

 but the real question is, whether these two processes of striating and 

 depositing were not going on simultaneously in the region generally, 

 though not at absolutely the same points. If the striae be due, as 

 some geologists have supposed, to detrital matter driven by a rapid 

 current, the two processes must of necessity have been simultaneous, 

 the one where the current was most rapid, the other where it was less 

 so. Or if we refer the strise in the lower and flatter regions of the 

 area of the drift to floating ice, how was it that the icebergs and the 

 currents which impelled them onwards bore no detrital matter at 

 that time, and so much at a subsequent time ? I conceive the two 

 processes to have gone on simultaneously. No agency for the pro- 

 duction of striated and polished surfaces has ever yet been suggested 

 which would not almost necessarily be accompanied with the trans- 

 port, and consequently with the deposition of detrital matter. Cur- 



