OF THE SEA AND LAND. 15 



how little it has yet clone in forming its own channel; 

 henceforth, with little exception, to flow in that bed 

 which rivers may truly he said to have formed for 

 themselves. The Forth presents a far longer course 

 of that repose which it has produced for itself; though 

 the well-known lakes among its sources mark the beds 

 which nature prepared for it, and which it has scarcely 

 yet impressed with the marks of change. And if we 

 desire to know the destruction which rivers produce 

 near their entrances into the sea, we can see that the 

 Tamar, the Fowey, and others, once joined it as rapid 

 torrents, if not as cataracts. A cataract in Sky now 

 plunges, a detached stream, over three hundred feet of 

 a perpendicular cliff; while, if the time will come when 

 it must enter a gentle stream, that change is already 

 commenced in a neighbouring one, which meets the 

 sea, a foaming torrent. 



Proceeding now to trace the great process of Pro- 

 duction, I have already shown that rivers carry to the 

 plains, and finally to the sea, the materials which they 

 have taken from the mountains. But that which they 

 take from one part of the earth to add to another, is 

 disposed of in different ways. At the upper levels, 

 these materials fill the higher valleys or modify their 

 forms; on the lowest, they generate plains; and, at 

 the entrance of the rivers into the sea, they produce 

 hanks and islands. In the courses of the streams, 

 they fill up lakes, becoming again known to us; but, 

 once deposited beneath the sea, if they do not cause 

 its bottom to rise above the surface, they are thence- 

 forward known only by the soundings of mariners. 

 Occasional events, however, accelerate and modify 

 these results. The torrent of an hour sometimes per- 

 forms the work of years: and inundations suddenly 

 raise the plains, or deposit banks and islands at the 

 actuaries of the streams: as thus also the feeble barrier 



