218 THE PHENOMENA OF DRIFT, OR 



tion of ice around the poles during the glacial period, only to the 

 thickness of a few thousand feet. This is certainly far too small 

 an amount to satisfy the above conditions. If we might suppose, 

 that as a consequence of the earth's ceasing to turn on its axis, 

 the water should accumulate, as it naturally would, around the 

 poles to the depth of thirteen miles, and become converted into 

 ice, and then upon the renewal of the earth's dim-nal motion and 

 the return of heat, be slowly melted away, we should have a 

 source whence water and ice could be made to flow southerly for 

 a long period. This supposition is, to be sure, a highly hypo- 

 thetical one ; and yet not impossible : nor can I conceive that the 

 glacier theory furnishes an adequate cause for glacio-aqueous 

 agency on this continent, till it shall point out an equally prolific 

 source of long continued cold, icebergs, and southerly cun-ents.* 

 Mr. Maclaren has recently suggested an ingenious amalgama- 

 tion of the iceberg theory of Lyell, with the glacier theory of 

 Agassiz, He has rendered it very probable, that if most of the 

 present continents of the globe were beneath the ocean, there 

 would exist a broad westerly current between the tropics, and two 

 easterly cmTcnts between the tropics and the poles. Such he 

 supposes to have been the state of the northern hemisphere during 

 the glacial period. He also supposes, with Agassiz, that during 

 the same time, there was a vast accumulation of ice around the 

 north ,pole ; which, upon the return of heat, would send off cur- 



* I regret to find tliat the President of the London Geological Society^ {see M: Miir- 

 chisoii's Address before thai Society in Fehrnary, 1S42,) has understood me in my Address 

 before the Association of American Geologists, to be committed to the unmodified glacier 

 theory of Agassiz. Much more do I regret, that he seems to identify the views of Amer- 

 ican geologists with mine. I did, indeed, express myself strongly in my admiration of the 

 ingenuity and ability with which the subject was treated by that distinguished naturalist, 

 and in my joy at the new light which the history of glaciers seemed to me to shed upon 

 the phenomenaof striated, smoothed, and embossed rocks, and the formation of moraines; 

 but I certainly never imagined that his theory, unmodified, would explain the phenomena 

 of drift in our country. And this I stated three times in that Address. I also stated what 

 was the grand conclusion to which my mind had come in view of all the facts ; namely, that 

 " glacio-aqueous action (by which I mean the joint action of ice and water, without deci- 

 ding which has exerted the greatest influence,) has been the controlling power in produ- 

 cing the phenomena of drift." My general views on this subject were the same when I 

 wrote my Address, as when I wrote this paper; except that in the latter, they are more 

 matured and carried out into details. 



