244 FRAGMENTS OF SCIENCE. 



Looking at the little glaciers of the present day 

 mere pigmies as compared to the giants of the glacial 

 epoch we find that from every one of them issues a 

 river more or less voluminous, charged with the matter 

 which the ice has rubbed from the rocks. Where the 

 rocks are soft, the amount of this finely pulverised 

 matter suspended in the water is very great. The 

 water, for example, of the river which flows from 

 Santa Catarina to Bormio is thick with it. The Ehine 

 is charged with this matter, and by it has so silted up 

 the Lake of Constance as to abolish it for a large frac- 

 tion of its length. The Rhone is charged with it, and 

 tens of thousands of acres of cultivable land are formed 

 by the silt above the Lake of Geneva. 



In the case of every glacier we have two agents at 

 work the ice exerting a crushing force on every point 

 of its bed which bears its weight, and either rasping 

 this point into powder or tearing it bodily from the 

 rock to which it belongs; while the water which every- 

 where circulates upon the bed of the glacier continually 

 washes the detritus away and leaves the rock clean for 

 further abrasion. Confining the action of glaciers to 

 the simple rubbing away of the rocks, and allowing 

 them sufficient time to act, it is not a matter of opinion, 

 but a physical certainty, that they will scoop out val- 

 leys. But the glacier does more than abrade. Rocks 

 are not homogeneous; they are intersected by joints 

 and places of weakness, which divide them into vir- 

 tually detached masses. A glacier is undoubtedly com- 

 petent to root such masses bodily away. Indeed the 

 mere a priori consideration of the subject proves the 

 competence of a glacier to deepen its bed. Taking the 

 case of a glacier 1,000 feet deep (and some of the older 

 ones were probably three times this depth), and allow- 

 ing 40 feet of ice to an atmosphere, we find that on 



