3 2o POPULAR SCIENCE MONTHLY 



cussion of the problems of the ice age, and to register again his opposi- 

 tion to the views generally held by American geologists. Many of the 

 arguments used closely resembled those of his former papers and may 

 be reviewed here for the last time. 



He regarded the phenomena of the boulder clay and drift in eastern 

 America as due to the action of local glaciers, drift ice and the agency 

 of cold northern currents. Against the theory of a universal glacier 

 he again argued on the ground that such suppositions were not war- 

 ranted by the facts. 



The temperate regions of North America could not be covered with a 

 permanent mantle of ice under existing conditions of solar radiation; for, 

 even if the whole were elevated into a tableland, its breadth would secure 

 a sufficient summer heat to melt away the ice except from high mountain peaks. 



For the supposition that such immense mountain chains existed 

 and have disappeared, he found no warrant in geology, and for such 

 an ' unexampled astronomical cause of refrigeration ' as the earth's 

 passing into a colder portion of space, he found no evidence in as- 

 tronomy. He agreed with Lyell in regarding the theory of the vary- 

 ing eccentricity of the earth as expounded by Croll as insufficient; 

 moreover, it seemed to him physically impossible that a sheet of ice, 

 such as that supposed, could move over an uneven surface, striating 

 it in directions uniform over vast areas and often different from the 

 present inclination of the surface. 



He was further influenced in his opinion by the work of Hopkins, 

 who showed, apparently, that only the sliding motion of glaciers could 

 polish or erode rock surfaces, and the internal changes in their mass — 

 the result of weight — could have little or no effect. Glaciers, more- 

 over, he argued could not have transported the boulders great distances 

 and lodged them upon the hill tops, and the universal glacier would, 

 moreover, have no gathering ground for its materials. The huge 

 feldspar boulders from the Laurentide Hills, stranded at Montreal 

 Mountain at a height of six hundred feet above the sea and from fifty 

 to sixty miles further southwest, and which must have come from little, 

 if any, greater elevation and from a direction nearly at right angles 

 to that of the glacial striae, were against the ice-sheet theory, as were 

 also the large boulders scattered through the marine stratified clays 

 and sands, and the occurrence of marine fossils in the lower part of 

 the drift in the true till near Portland, Maine, and at various points 

 on the St. Lawrence in Canada. 



To substantially these views Dawson held to the very last. In his 

 ' Ice Age in Canada' (1893) he is found still combating vigorously 

 the idea that all northern Europe and America were covered by a mer, 

 de glace moving to the southward and outward to the sea, and which 

 moved not only stones and clay to immense distances, but glaciated and 



