Outlines of Geology, 89 



ing the adjacent lands of their water, and carrying it in brooks 

 and streamlets, which gradually unite to form rivers, and ulti- 

 mately convey their contents into the ocean, of which, in fact, they 

 constitute a series of ascending branches. 



Now there are some valleys and river channels which appear to 

 owe their origin to some great convulsion or catastrophe, which 

 has torn asunder the rocks and strata, and left certain intervening 

 chasms ; but in by far the greater number of instances we have 

 no evidence whatever of the activity of such agents, and every 

 thing indicates a less sudden and violent, but yet an energetic, 

 cause. 



Valleys frequently intersect the strata which they traverse, in 

 such a way as to leave no doubt of their subsequent formation to 

 that of their bounding rocks, a phenomenon almost always observ- 

 able, and sometimes within very narrow limits ; as where in a 

 mountainous country a rapid river cuts through a narrow defile ; 

 on these occasions we observe the same strata repeated upon each 

 wall, as it were, of the valley, the soil or substratum of which con- 

 sists of the lowest layer of the series. Now when we witness 

 such appearances, and when among the pebbles, and sand, and 

 fragments of the low-land we find comminuted portions of the 

 surrounding rocks, when we discover a collection of such debris in 

 the soil and bed of the river, we almost necessarily arrive at two 

 conclusions ; one, that the strata once were continuous ; and the 

 other, that the intersecting agent has been water : water, not 

 flowing as it now does, quietly through the valleys, but constituting 

 mighty and destructive torrents, which, while they have inter- 

 sected, have at the same time, in many instances, denuded the 

 strata ; which sometimes working upon soft or muddy materials, 

 have transported them to a distance, but which have also ground 

 down the hardest substances, and aided by the gravel and debris 

 thus formed and impetuously hurried along, have chiselled out fur- 

 rows in the more indurated and primary rocks. Some have vainly 

 imagined the present streams as adequate to the production of such 

 effects ; but he whose sight is not dimmed by hypothetical blind- 

 ness, will see evidences of a more powerful agent, and will at 



