a. XXIL] 



DENl'DING AND TRANSPORTING AGENTS. 



571 



remove 





matter from above to below the sea level, is insignificant in 

 comparison with the power of rivers to perform the same 

 task. As an illustration we may take the coast of Holder- 

 ness, described in Chap. XX. (p. 510). It is composed, 

 as we have seen, of very destructible materials, is thirty-six 

 miles lono-, and its average height may be taken at forty feet. 

 As it has wasted away at the rate of two and a quarter yards 

 annually, for a long period, it will be found on calculation 

 that the quantity of matter thrown down into the sea every 

 year, and removed by the current, amounts to 51,321,600 cubic 



feet. 



It has been shown that the united Ganges and Brahma- 

 pootra carry down to the Bay of Bengal 40,000,000,000 

 of cubic feet of solid matter every year, so that their trans- 

 porting power is no less than 780 times greater than that of 

 the sea on the coast above mentioned ; and in order to pro- 

 duce a result equal to that of the two Indian rivers, we must 

 have a line of wasting coast, like that of Holderness, nearly 

 28,000 miles in length, or longer than the entire circum- 

 ference of the globe by above 3,000 miles. The reason of so 

 great a difference in the results may be understood when we 

 reflect that the operations of the ocean are limited to a single 

 line of cliff surrounding a large area, whereas great rivers 

 with their tributaries, and the mountain torrents which flow 

 into them, act simultaneously on a length of bank almost 



indefinite . 



Nevertheless we are by no means entitled to infer, that the 

 denuding force of the great ocean is a geological cause of 

 small efficacy, or inferior to that of rivers. Its chief influence 

 is exerted at moderate depths below the surface, on all those 

 areas which are slowly rising, or are attempting, as it were; 

 to rise above the sea. From data hitherto obtained respect- 

 ing subterranean movements, we can scarcely speculate on an 

 average rate of upheaval of more than two or three feet in a 



century. 



An elevation to this amount is taking 

 i?< aTirl -nrnhnblv in manv submarine are 



place 



as those which we know to be sinking from the proofs de- 

 rived from circular lagoon islands or coral atolls.* 



* See the last chapter in Vol. II. 



