GLACIAL EROSION AND TRANSPORTATION. 279 



that it does not conform to the law of oilier moving fluids. 

 Probably there is no reason why an ice-cascade should not 

 produce results of erosion analogous to those of a waterfall. 



Summarily stated, our conclusions are that, like every- 

 thing else connected with the action of such a complicated 

 cause as that brought into view in the production of glacial 

 phenomena, the exact extent of its erosive and transporting 

 power is difficult to determine. The action of ice over the 

 glaciated region took place after other forces had been in full 

 operation during long ages ; and hence it is often impossible to 

 separate the effects of the second cause from those of the first. 



But there can be no doubt that running water is by far 

 the most efficient of all eroding agencies which have given 

 shape to the contour of the continents. Most important re- 

 sults follow from the power of water to act as a solvent. 

 Extensive regions have been undermined and lowered 

 through the removal by water of the soluble salts. Such has 

 perhaps been the origin of many of the valleys of the Appa- 

 lachian region and of some of the great lakes of the world. 

 Running water is also a most effective mechanical agency, 

 continually acting along the natural lines of drainage. The 

 sand and gravel rolled along over the bottom of a rapid 

 stream of water act like a rasp or a saw, and have everywhere 

 worn deep narrow channels across the slowly rising mountain- 

 chains. Water as an eroding agency has had a great advan- 

 tage over ice in the far greater length of time during which 

 it has been in the field to operate. 



Still, it can not be doubted that ice has had no small part 

 in transforming the appearance of the portions of the world 

 to which it has had access. Of this the evidence is abundant 

 in the great number and size of the bowlders scattered over 

 the glaciated region, hundreds of miles from their native 

 ledges, and weighing hundreds and even thousands of tons. 



Inasmuch as ice is frozen water, its melting furnishes the 

 torrents to aid in the transportation. The finely comminuted 

 material ground up underneath the kw i« largely carried away 



