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THE POPULAR SCIENCE MONTHLY. 



showing their contour and the areas covered 

 by their ice-sheets. Mr. Kendall fully sus- 

 tains the conclusions of the late Prof. Henry 

 Carvill Lewis, that the British drift was due to 

 land ice, with no considerable marine sub- 

 mergence of any part of these islands. The 

 marine shells, mostly fragmentary, which are 

 found up to the height of about fourteen hun- 

 dred feet on Moel Tryf aen, are confidently as- 

 cribed to currents of the ice-sheet flowing 

 southward over the bed of the Irish Sea, 

 plowing up its marine deposits and shells and 

 carrying them upward as glacial drift to this 

 elevation. 



Norway, Sweden, and Denmark, the North 

 Sea and the Baltic, northern Germany, and a 

 large part of Russia, were enveloped by an 

 ice-sheet which flowed radially outward from 

 the Scandinavian mountains and plateau. 

 Bowlders of Scandinavian rocks were brought 

 across the present area of the North Sea to 

 Yorkshire in England. Moraines of this ice- 

 sheet have been traced across Germany by 

 Prof. R. D. Salisbury, who finds them closely 

 like the moraines that he had previously ex- 

 plored in the northern United States. 



Many relics of palaeolithic man, contem- 

 poraneous with the Glacial period and with 

 numerous extinct species of animals, have 

 been found in river gravels and in caves in 

 Wales, England, France, Belgium, and Ger- 

 many, which Prof. Wright has well described. 

 He does not proceed, however, to treat of the 

 neolithic and later races of men, who have 

 inhabited Europe since the Ice age. The gla- 

 cial type of man is represented by portions of 

 skeletons, including skulls, exhumed many 

 years ago in Canstadt and Neanderthal, Ger- 

 many, and recently by Profs. Lohest and Frai- 

 pont in the commune of Spy, Belgium. 



The author believes that all the phenom- 

 ena of the drift can be better explained by a 

 single Glacial epoch than by two or several 

 such epochs divided by long intervals of mild 

 or warm climate. In this opinion he differs 

 from most American glacialists, from Prof. 

 James Geikie and others in Great Britain, 

 Wahnschaffe in Germany, Penck in Austria, 

 and De ,Geer in Sweden ; but is in agreement 

 with Lamplugh in England, Falsan in France, 

 and Hoist in Sweden, who attribute the fos- 

 siliferous beds inclosed between deposits of 

 till to oscillations of the front of the ice, 

 rather than to its complete departure and re- 



turn. " So far as we can estimate," says 

 Prof. Wright, " a temporary retreat of the 

 front, lasting a few centuries, would be suffi- 

 cient to account for the vegetable accumula- 

 tions that are found buried beneath the gla- 

 cial deposits in southern Ohio, Indiana, cen- 

 tral Illinois, and Iowa, while a temporary re- 

 advance of the ice would be sufficient to bury 

 the vegetable remains beneath a freshly ac- 

 cumulated mass of till." With reference to 

 the argument for two distinct glacial epochs 

 in North America drawn from the greater oxi- 

 dation of the clays and the more extensive 

 disintegration of certain classes of the bowl- 

 ders found over the southern part of the gla- 

 ciated area, attention is directed to the super- 

 ficial decay of the rocks before the Ice age, 

 like that now observed outside the drift re- 

 gion. " There was an enormous amount of 

 partially oxidized and disintegrated material 

 ready to be scraped off with the first advance 

 of the ice, and this is the material which 

 would naturally be transported farthest to 

 the south ; and thus, on the theory of a sin- 

 gle Glacial period, we can readily account for 

 the greater apparent age of the glacial debris 

 near the margin. The debris was old when 

 the Glacial period began." 



As to the causes of the Ice age, the au- 

 thor points out strong objections against the 

 astronomic theory which has been so ably 

 advocated by Croll, Geikie, and Ball. Meas- 

 urements of the rates of erosion of the gorges 

 below the falls of Niagara and of St. Anthony, 

 as shown by Gilbert and Winchell, allow us 

 no more than seven thousand to ten thousand 

 years since the end of the Glacial period, in- 

 stead of the eighty thousand years required 

 by Croll's theory. Geographic conditions 

 seem more likely to have produced the gla- 

 cial climate, continental ice-sheets, and for- 

 merly more extensive glaciers on mountain 

 ranges. According to Dana, Upham, Le 

 Conte, Jamieson, and others, submarine river 

 channels and fjords, reaching down three 

 thousand to four thousand feet beneath the 

 sea-level, prove that these glaciated areas 

 were greatly uplifted, probably attaining such 

 altitudes that their precipitation of moisture 

 was mostly snow throughout the year; and 

 the snow and ice may have been more rap- 

 idly accumulated because of changes in the 

 oceanic circulation by submergence of the 

 Isthmus of Panama. 



