254 PROFESSOR JAMES GEIKIE, LL.D., D.C.L., F.R.S., ETC., ON 



COMMUNICATION" 



From Mr. Warren Upham ; Assistant, United States Geological 

 Survey. 



The very important Paper by Professor Geikie I have read 

 with the greatest interest, since his conclusions as to the prob- 

 able causes of the accumulation of the ice-sheets of the Glacial 

 period differ so widely from the views which from much observa- 

 tion and study I have come to hold with a good degree of confi- 

 dence. He has devoted this Paper to the exposition of the difficulties 

 and objections which beset my explanation of ice-accumulation as 

 due to climatic conditions, chiefly the prevalence of snowfall during 

 nearly all the year, attendant upon great elevation of the regions 

 that became glaciated. 



Most of these difficulties I cheerfully acknowledge, and yet think 

 that the evidences of such Pleistocene elevation of North America 

 and North-Western Europe are decisive. The researches of N. H. 

 Winchell, McGee, Chamberlin, Salisbury, Leverett, and myself, in 

 the United States indicate the divisibility of the Glacial period 

 into at least two epochs of glaciation, divided by a long interglacial 

 epoch, when the North American ice-sheet may have been entirely 

 melted away. We thus agree with Professor Geikie, the late Dr. 

 Croll, Wahnschaffe, Penck, De Geer, and other European glacialists, 

 who find similar proofs of two or more glacial epochs, separated ty 

 intervals of mild climate. This repetition of the conditions pro- 

 ducing ice-accumulation is justly insisted on by Professor Geikie as 

 the strongest objection that can be urged against its explanation 

 by high uplifts of the land. The relationship, however, which I 

 suppose to have existed between the earth's contraction and the 

 processes of mountain-building, whereby the earth-movements pro- 

 ducing high altitude and glaciation were induced, may well have 

 caused ice-sheets to be accumulated successively upon various parts 

 of the earth's surface, not necessarily nor indeed probably existing 

 at the same time upon all drift-bearing countries ; and after an 

 interglacial epoch, the same conditions might, as I have shown, be 

 renewed upon any given area, as in North America and North- 

 Western Europe. The supposed difficulties on account of widely 

 distributed areas of glaciation and repetitions of ice-accumulation 

 are duly considered in my Probable Causes of Glaciation, published 



