ON THE ACTION OF RIVERS. 441 



appear too great for those small streams that meander at 

 their feet, what cannot be attributed to their immediate 

 power is attributed to the continued action of time. 



Without examining how long a series of ages it would 

 be necessary to admit, before the rivers which we have 

 mentioned above, and the water-courses encased in the 

 deep valleys of the Alps, Pyrenees, Jura, Grampians, &c. 

 could have scooped their valleys, on which their present 

 action is so slow that no one has yet been able to estimate 

 it ; without examining if this long series of ages agrees 

 with the phenomena, which preclude our attributing so 

 remote an antiquity to the actual state of the earth's sur- 

 face, a question of too much importance to be treated in- 

 directly ; it will be sufficient to mention here four sorts 

 of observations, in order to be persuaded, or at least 

 to suspect, that the present rivers, even supposing 

 them ten times the size that they are, could not have 

 scooped ' out the deep channels at the bottom of which 

 they run. 



1. We must recur to the period when the ranges of 

 hills which border the present valleys were not as yet 

 scooped out, but were united in such a manner as not 

 to leave any hollow between them, or merely a slight ori- 

 ginal depression. 



This shallowness of the valley would be accompanied 

 with an inconsiderable slope of its bottom. If, then, we 

 suppose the same mass of water, it must run with less 

 quickness, and consequently with much less power ; and 

 yet a very great force must be attributed to it, before 

 it could have had the power of removing a portion of 

 rock nearly represented by a recumbent triangular prism, 

 having often 500 metres of breadth by a sometimes equal 



