and the Effects of Glacial Action, 291 



from their agency alone that the most important changes in 

 the earth's surface have been effected, and that the opposition 

 made to it proceeds from a misapprehension of the power of 

 water, we shall endeavour to point out two assumptions which 

 appear to have been taken as facts, or as axioms whereon to 

 build a demonstration, instead of considering them merely as 

 propositions to be proved. 



The opponents of the glacial theory assume, as the basis of 

 their arguments, 



Ist^ That water has an abrading action upon rocks. 

 2dly, That stones, propelled by water, can make furrows 

 and scratches upon rocks wath which they may come in con- 

 tact, similar to those which are made by stones propelled by 

 glaciers. 



If water has the abrading power which some attribute to it, 

 we should not fail to find at the mouths of rivers which have 

 run for a considerable distance over a gravelly bed, some indi- 

 cations in the water of the abrasion ; and we should find the 

 most perfect specimens of rounded stones at the mouths of 

 rivers ; and, as we ascended the stream, we should find them 

 becoming less and less rounded, the most angular and irregular 

 in shape being at the source. Now, neither of these is the 

 case. The water at the mouths of rivers with gravelly beds 

 (except in times of floods) is as free from particles of stone as 

 when it issues from its spring, and the gravel there is as round 

 and smooth as at its mouth. The effects produced upon rocks 

 which intercept the passage of a river, we have not overlooked. 

 Some are worn, and the stream rushes through the cavity or 

 fissure formed ; others are covered with a vegetable substance, 

 and the rock beneath is as rough as on the day it was first 

 bared. In the former case, the stream has descended over a 

 gravelly bed, and we conclude that the fissure has been formed 

 from the attrition of the stones which the water may have 

 brought down with it in its floods ; and, in the latter case, 

 it has descended over a sandy bottom, from which we conclude, 

 that so little abrasive power has the water, even when charged 

 with particles of sand, that it does not prevent the seeds of 

 plants germinating upon the rock. 



