394 CLIMATIC CONDITIONS OF THE GLACIAL EPOCH. 



of boulders, having apparently no recognition of the fiict that there is any 

 erosive and transporting agent except ice. Such an idea cannot be admitted 

 as having the slightest claims to consideration. One must be blind not to 

 see that the bulk of the water-worn boulders and pebbles formed at the 

 present time in glacier regions consists simjoly of material thrown down in 

 an angular form on the glacier, carried upon its surface in the same con- 

 dition, and dumped at its terminus, where it remains unchanged initil water 

 has access to it, and deprives it of its morainic character. The ice is not by 

 any means the real agent of the formation of the bouldei', which woidd have 

 lost its angular shape and acquired a rounded form whenever exposed to the 

 action of water had there been no glacier in its way to receive it when it 

 was loosened from the overhanging rocky wall and fell downward into the 

 v.alley. 



When we take into consideration the relative positions of the land masses 

 of the two hemispheres, the peculiar conditions of things in the southern, 

 and the very different extent to which various portions of the northern are 

 covered by snow or ice, it seems impossible to admit lor a moment that 

 astronomical causes of the kind indicated by Adhemar or Croll can at the 

 present time have any perceptible influence on the glacial conditions of those 

 regions. And if they are not now thus influential, so there is every reason 

 to believe that they were inoperative in the past. The weight of the highest 

 authorities is decidedly against the theories of Ijoth Adhemar and Croll from 

 the stand-point of astronomical science ; while it is believed that these 

 theories are equally at variance with the conclusions of the most eminent 

 climatologists of the present day. At all events, the evidence in favor of 

 a cyclical recurrence of cold or glacial periods sinks into insignificance Avhen 

 compared with that indicating a progressive diminution of the temperature 

 on the earth's surface during the geological ages, and from the very earliest 

 times when land began to exist from the conditions of which light on this 

 subject could be procured. 



