14 R. M. Deeley — North American 



with terrestrial rnovements which have occurred from time to time 

 tliroughout all geological history. But, in order to measure the 

 movements, it lias been necessary to recognize the level of the ocean 

 as a datum for reference in accordance with the views of our great 

 master Lyell. But I would only point out that however great the 

 oscillatious of the crust may appear to us living on its surface, 

 they will appear extremely diminutive when measured by the length 

 of the earth's radius, which is the true standard of measurement. 



V. — North American and European Drift Deposits. 

 By E. M. Deeley, M.Inst.C.E., F.G.S. 

 (WITH A FOLDING TABLE.) 

 ^MHE classification of the drift deposits is one which has given rise to 

 1_ very divergent views. One school holds that the Glacial Period 

 was marked by increasingly severe conditions of climate followed bv 

 a somewhat regular amelioration. Another school holds that it 

 consisted of a series of cold periods separated by warm intervals. It 

 is not contended that in Pleistocene times the ice disappeared 

 completely; for it is pretty certain that on high mountain ranges, and 

 in the Arctic and Antarctic areas, snow-fields and glaciers existed 

 continuously. With cold conditions the ice-covered regions spread 

 from the Polar areas and glaciers descended from the mountains, and 

 with the return of warmer conditions the Polar glaciers and ice-fields 

 decreased in area whilst the mountain glaciers again retreated up the 

 valleys. The problem as to the extent to which such variations in 

 glacial conditions occurred, and the number of times they recurred, 

 can only be settled by a study of the Pleistocene deposits themselves. 

 In this matter theorj' cannot at present help us. 



During recent rears much work has been done wliich has an 

 intimate bearing upon the question, and several geologists have given 

 their views on the subject of the classification of the drifts. In 

 iNortli America, where drift deposits are especially well developed, 

 our knowledge of them lias been greatly increased by the work of 

 Salisbury, Chamberlin, Calvin, Wiedman, Upham, Calhoun, Tarr, 

 Gilbert, Coleman, Stone Alden, Leverett, and many others. In the 

 European Alps and North-West Europe, Penck, Bruckner, Suess, 

 Hess, Forel, Wahnschafi^e, Keilack, French, Credner, Emil Werth, 

 Klantzsch, Berg, and many others have done a great deal in the 

 classification, description, and mapping. 



In 1895 James Geikie ' gave us a classification of the glacial deposits 

 in which he attempted a correlation of the North American with the 

 European deposits, whilst Frank Leverett- in 1910, in the light of 

 more recent work, has again dealt with the question in some detail. 

 His paper is printed in English. 



Leverett spent the year 1908 in Western Europe in a study which 

 had for its aim a comparison and tentative correlation of the glacial 

 deposits in that area with those of the United States, on the study of 



^ Journal of Geology, vol. iii, pp. 241-69, 1895. 



• Zeitschrift filr Gletscherkunde, vol. iv, pp. 242-95, 321-42, 1909-10. 



