560 Sohitions from, 



If we could take all the rivers of the world into the 

 calculation, how great the amount must be. The St. 

 Lawrence alone drains an area of 297,600 square miles, 

 three and a third times larger than the whole of Great 

 Britain, and that of the Mississippi is 982,400 square 

 miles, or more than three times as large as the area 

 drained by the St. Lawrence. The Amazon drains an 

 area of 1,512,000 square miles, but it is needless to 

 multiply cases. 



It is a necessary part of the economy of Nature that 

 this dissolving of the constituents of rocks should 

 always be going on over all the world, for it is from 

 solutions of lime and oth'er salts thus obtained by the 

 sea, that plants and shell-fish derive part of their 

 nourishment, plants for their tissues, and Mollusca and 

 other creatures for their shells and bones. As it is now, 

 so has it been through all proved geological time, and 

 doubtless long before ; for the oldest known strata, the 

 Laurentian rocks, were themselves originally formed 

 of ordinary sediments, and consist in part of thick 

 strata of limestone that must have been formed by the 

 life and death of organic creatures in the sea. 



This waste of material by the dissolving of rocks is 

 indeed evident to the practised eye over most of the 

 solid limestone districts of England, and I shall there- 

 fore say a little more on the subject. On the flat tops 

 of the Chalk Downs, for example, over large areas in 

 Dorsetshire, Hampshire, and Wiltshire, quantities of 

 angular unworn flints, many feet in thickness, com- 

 pletely cover the surface of the land, revealing to the 

 thoughtful mind the fact, that all these accumulations 

 of barren stones have not been transported from a dis- 

 tance, but represent the gradual destruction by rain 

 and carbonic acid, of a vast thickness of chalk with 



