44 ON THE GENERAL DISPOSITION OF THE 



abrupt mountainous regions, the vallies are conse- 

 quently deep, with steep sides, often precipitous or 

 rocky. In these cases, they are frequently also very 

 narrow ; the opposite sides meeting below, without an 

 intervening flat ; and forming that variety well ex- 

 pressed by the Scottish term glen. If the bottom has 

 an uniform declivity, the valley then give passage to a 

 permanent stream or occasional torrents ; if curved, it 

 becomes the seat of a mountain lake. 



Where the declivity of the bottom of such a valley 

 is gentle, and especially where the breadth is consi- 

 derable, alluvial matters in time accumulate on the 

 lower parts, and thus a plain is formed within it ; 

 producing that peculiar variety of shape distinguished 

 by the Scottish term Strath. Lastly, in lands of lower 

 undulation, the valley expands until its peculiarity is 

 at length lost in the gently undulating plain. It will 

 be a subject for future inquiry, how far the forms or 

 the existence of vallies have been the consequence of 

 the action of rivers. 



Of Springs, Rivers, and Lakes. 



The nature and existence of Springs, as forming 

 the origin of rivers, is one of those circumstances in 

 the physical history of the earth which is peculiarly 

 connected with the phenomena of Geology. But it 

 is a very obscure subject, and one respecting which 

 we can, in many instances, scarcely form a rational 

 conjecture. 



It is a common remark by writers on this subject, 

 that springs abound most in mountainous countries, 

 and that they break out at the feet of the declivities. 

 This assertion is far from being generally true ; parti- 

 cularly if we include those which, from the peculiar 

 nature or declivity of the surface, are unable to reach 



