THE BUILDING OF THE EARTH 



draining an area of 30,000 square miles, discharges 

 1,510,137,000 cubic feet of sediment annually. This is 

 equivalent to a lowering of its whole drainage area 

 by T^th of a foot per annum, so that in a thousand 

 years the whole area over which it flows has been lowered 

 by the river by more than a foot. The Thames alone 

 carries down 5,000,000 tons of material each year. All 

 this must be redeposited somewhere. Where the re- 

 deposition takes place we find new land forming, new 

 beds, new strata, in which in ages to come the future 

 tenants of the globe may find relics of the people and 

 animals living to-day. 



Thus there are several evident ways in which the 

 coast-line of a country might be altered, either in the 

 direction of enlarging its boundaries by additions to it 

 made by the sea or by rivers; or in the direction of 

 losing parts of its territory by wear and tear. But 

 there are other changes going on which are not so easy to 

 perceive, and which are not so easy to account for. The 

 thing hardest to explain is why what is now dry land 

 should have risen out of the sea, as certainly it did. The 

 white cliffs of Dover are made of chalk, and chalk is 

 made of innumerable shells of tiny animals which once 

 lived in the sea and which at their death sank to the 

 sea's bottom. They steadily accumulated there for ages 

 in a grey ooze, and in course of time this grey ooze rose 

 above the waves. It dried and became land. But chalk 

 is not found in cliffs by the sea only. It is found far 

 inland. It is found, for example, in the North Downs, 

 which run from Guildford to Reigate and from Reigate 



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