248 ACTION OF 



vide the rivulet with water. In rivers of longer 

 course, that is more striking. Take, for instance, 

 the Thames ; the quantity of water that rises up 

 in the springs, though much magnified in the pic- 

 torial representations, is in reality considerable : 

 but look at the distance to the sea, and think 

 whether, instead of that infant stream having ex- 

 cavated the goodly valley of which it is now the 

 wealth and the ornament, it must not have been 

 evaporated before it could have reached Windsor 

 or even Oxford. 



That a river can cut deeply, even into very hard 

 strata, is proved by many instances ; but in those 

 instances there are always slopes above to send 

 down in a flood, during rains, that water which, if 

 it fell on level ground, would sink into the earth, 

 and not form any flood at all : so that there could 

 be no cutting through even the softest materials. 

 These cuttings are, in general, the secondary 

 strata, or even collections of rubbish; and there 

 is perhaps no instance of a dell formed by the ac- 

 tion of water wholly in the solid granite, though 

 in many places there are little notches. The 

 cutting of the rubbish may go on very rapidly, so 

 that a large excavation may be made in a year, or 

 even a day; but the solid and seamless rock is 

 quite another matter, and we find that even a con- 

 siderable river, with the assistance of a valley 

 every way well adapted for the producing of 

 powerful floods, makes but little impression on 

 such strata in the course of ages. 



The North Esk, which discharges its waters into 

 the British ocean, a few miles to the northward 

 of Montrose, and the Isla, which flows by the 

 castle of Airlie, from the southern slope of the 



