RIVERS. 237 



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 considerable river, with the assist- 

 ance of a valley every way well adapted for the pro- 

 ducing of powerful floods, makes but little impres- 

 sion 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 Grampians to 

 'the valley of Strathmore, are perhaps two of the 

 most striking instances of rivers cutting the soil 

 that are to be met with in Britain. Both rivers 

 drain mountain valleys, the sides of which are steep, 

 and the autumnal rains fall very heavily on both. 

 There is no lake on the Isla to regulate the waters 

 when the rains fall, and on the North Esk there is 

 but one small one (Loch Lee), which is far in the 

 mountains near the source of the river, and has little 

 influence on the whole stream, because a great part 

 of the water of floods comes into the channel lower 

 down. 



Each of those rivers has cut a dell, or den, several 

 miles in length, and very deep in proportion to its 

 width. But gravel and red sandstone (which in 

 those places is a soft crumbling stone, together with 

 pudding-stone, very weakly cemented) are the prin- 

 cipal matters through which these rivers have cut. 

 Even now the cuts which they have made are little 

 more than sufficient for containing the flood water 

 during the rains. Gannachie bridge is thrown 

 across the dell of the Esk, among the very pictu- 

 resque scenery at " The Burn ;" and though, in com- 

 mon states of the river, the roadway on the bridge 

 be at least fifty feet above the water, the floods ris 

 BO high that a tall man of the village, locally named 

 "Lang Gannachie," could reach over the parapet 



