On Drift. 17 



coarse materials ; the second one of tranquil deposition ; and the 

 third was again a period of transport of large blocks and coarser 

 matter. This generalization appears to have been principally 

 founded on the characters of the drift of Lake Champlain and that 

 of the general valley of the St Lawrence, where the beds of the 

 second period not only consist, in great part, of finer matter, but 

 are also, in many instances, distinctly stratified, and filled with or- 

 ganic remains. But before we can adopt these subdivisions of the 

 general period with reference to so many distinct modes of action 

 of the transporting agencies, or of the different degrees of intensity 

 with which they acted, it will be necessary to prove the above-men- 

 tioned succession of beds to be general and not merely local. If local, 

 I should be disposed to refer the tranquil deposition of the fossili- 

 ferous and associated beds, partly at least, to the condition of a 

 deeper abmergence than at the periods of the transport of the 

 coarser beds and blocks above and below the finer beds. I see no 

 reason, in local facts of this kind, to infer that there were three dis- 

 tinct periods with reference to the intensity or mode of action of 

 the dispersing forces. I may here observe that Dr Bigsby de- 

 tected no evidence of this subdivision of the drift in the region 

 which he examined further to the west. 



Some of the American geologists appear to have entertained the 

 opinion that the Mastodon existed in that region after the latest 

 period of the drift, and seem to refer its final destruction to some 

 upheaval of the American continent. It may be doubted, how- 

 ever, whether any evidence has been offered of the existence of 

 that animal later than the latest drift in which its remains are 

 found ; nor do I understand how the cause just assigned could ef- 

 fect its final extinction. If, however, we admit the submergence 

 of that continent to the extent which many geologists are now dis- 

 posed to admit, there can be no difficulty in explaining the ex- 

 tinction of any of the great pachyderms which might have pre- 

 viously inhabited that region.* 



II. On the Causes of Change in the Earth's Superficial 

 Temperature. 

 The next paper to which I shall call your attention, although 

 not directly on the subject of the drift, may be considered as closely 

 associated with it, one of its principal objects being to account for 

 the peculiar climatal conditions of the glacial period — that period 

 to which geologists now universally refer the general phenomena 

 of drift. I allude to the paper which I have myself brought re- 



* To this account of Drift, there follow in the Address, numerous details re- 

 garding the drift of North America, Europe, and Australia, for which we have 

 no spare space at present. The alluvial gold of the Diggings — the curse of our 

 time — is noticed as to priority of discovery. Geologists appear to have had 

 little to say in this business — and so much the better. — Editor. 



VOL. LIII. NO. CV. — JULY 1852. B 



