238 GRAVEL. 



of the bridge and fill a bucket of water. The strata 

 through which the Isla has cut become hard more 

 gradually than those at the Esk ; so that the floods 

 in the dell at Airlie do not rise to such a height as 

 those in that at the Burn ; though in late harvests, 

 which are generally those that are more than usu- 

 ally 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 Agri- 

 cola led his Romans through that part of the coun- 

 try. Those linns, too, do not fall over granite, but 

 over secondary rocks of some description or other 

 partly hard pudding-stone and partly schistus ; so 

 that in the formation farther up, whether of the stra- 

 tified 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 ac- 

 tion not carried on entirely under water. Any situa- 

 tion in an alluvial country will suffice for enabling 

 one to understand that. Go, for instance, to any of 

 the heights near London, which command 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 Richmond Hill, and all the successive 



