WARREN UPHAM, ESQ., ON CAUSES OF THE TCE AGE. 207 



and the recent determinations of the geologic brevity of tlie 

 time since the ice-sheets disappeared from North America 

 and Europe, make it clear, in the opinions even of some 

 geologists who believe in a duality or plurality of Quaternary 

 glacial epochs, that not astronomic but geographic causes 

 produced the Ice age. From the meteorologist's standpoint 

 this astronomic explanation of a formerly glacial cHmate in 

 now temperate latitudes has been alternately defended and 

 denied,* just as geologists have been divided in respect to 

 its applicability to the history of the Glacial period. 



13 Many eminent glacialists, as James Geikie, Wahnschaffe, 

 Penck, De Ge^r, Chamberlin, {Salisbury, Shaler, McGee, 

 and others, believe that the Ice age was complex, having 

 two, three, or more epoclis of glaciation, divided by long 

 interglacial epoeh.s of mild and temperate climate Mdien tue 

 ice-sheets wert* entirely or mainly melted away. Professor 

 (.Ttikie claims five distinct glacial epochs, as indicatt.'d 

 by fossiliferous beds lying between deposits of till or 

 uiistratified ghuial drift, and by other evidences of great 

 climatic changes. Mr. McGee, in the United States, re- 

 cognizes at least three glacial epochs. On the other hand, 

 the reference of all the glacial dritt to a single epoch of 

 glaciation, with moderate oscillations of retreat and re- 

 advance of the ice-border, is thought more probable by 

 Dana, Hitchcock, and Wright in America, Prestwich and 

 Lamphigh in England, Ealsan in France, Hoist in Sweden, 

 and Nikitin in Kussia. To myself, though lormerly 

 accepting two glacial epochs with a long warm interval 

 between them, the essential continuity of the Ice age seems 

 noAv the better provisional hypothesis, to be held with 

 candour for weighing evidence on either side. The argu- 

 ments supporting this opinion are well stated by Prof 

 G. Frederick Wright in his works on the Ice Age. in JS'ortli 

 Awerica (1<!'89), and Man and the Glacial Feriod (1892), and 

 especially in articles in the Ameiiccai Journal of Science for 

 November, 1892, and March, 1894. 



14 In accordance with Dr. Crolfs astronomic theory, glacial 

 periods would be expected to recur with geologic frequency, 

 Avhenever the earth's orbit attained a stage of maxinnuu 

 eccentiicity, durir.g the very long Tertiary and ]\lesozoic eras, 



* One of the most adverse criticisms is by the Eu?sian meteorologist 

 and geographer, Dr. A. Woeikof, in the Am. Jour, of tScience, third serie.s, 

 vol. xxxi, pp. 161-178, March, 1886, 



P 



