250 GRAVEL. 



usually rainy, both rivers do considerable damage 

 to the crops and fields in the plains below. 



But those rivers, notwithstanding the headlong 

 impetuosity of their floods, and the traces of their 

 devastation in those channels, have done very 

 little within the period of their recorded history ; 

 and probably the " linns," or cascades, where 

 the hard strata have resisted the action of the 

 water, are nearly in the same places as they were 

 when Agricola led his Romans through that part 

 of the country. Those linns, too, do not fall over 

 granite, but over secondary rocks of some de- 

 scription or other partly hard pudding-stone and 

 partly schistus ; so that in the formation farther 

 up, whether of the stratified or the granular stone, 

 the rivers could have had very little to do. 



Even in cases where there are no rock founda- 

 tions with which to contend, it is quite impossible 

 to account for the form of the present surface, by 

 any action of the waters now existing, or by any 

 action not carried on entirely under water. Any 

 situation in an alluvial country will suffice for 

 enabling one to understand that. Go, for instance, 

 to any of the heights near London, which com- 

 mand a view of that part of the valley of the 

 Thames, examine the position of the gravel and 

 clay hills on both sides, and then say whether, 

 trifling as they are, they could have been formed 

 by any action of the Thames, and of the ocean 

 jointly, working at the surface, even when the sea 

 may have flowed as far in as Teddington, or even 

 farther. What action of the river, and of the 

 resisting sea jointly, could have raised up Rich- 

 mond Hill, and all the successive swells or "caps" 



