8 Waste of Sea Cliffs. 



particles near the shore, while the finer and lighter 

 matter will often be carried out by the current and de- 

 posited further off. Then another layer of sediment 

 may be deposited on the top, and another, and another, 

 until, in the course of time, a vast accumulation of 

 strata may be produced. 



In this manner deltas are formed, and wide bays and 

 arms of the sea have been thus filled up. As they fill, 

 the marshes spread further and further, and, by over- 

 flows of the river bearing sediment, the alluvial flats 

 rise higher and higher, till, as in cases like those of the 

 Granges and the Nile, kingdoms have been founded on 

 mere loose detritus. A little reflection, too, will show 

 that all lakes, be they ever so large, may, with sufficient 

 time, get filled by this process with debris and become 

 plains. Some of the old rocks of Britain are formed of 

 sediments originally deposited in estuaries by rivers as 

 large as the Mississippi or the Granges, others were 

 formed in lakes fresh or salt, bearing witness to ancient 

 extinct physical geographies ; and many a modern flat 

 surface in Britain and in Switzerland, often covered by 

 peat and traversed by a brook or a river, is only a lake- 

 hollow filled with river-borne gravel, sand, and mud, 

 overgrown by a marshy or peaty vegetation. 



Again, if we examine sea-cliffs that rise direct from 

 the shore, we find that the disintegrating effect of 

 the weather produces frequent debacles great or small on 

 the faces of the cliffs, thus supplying material for the 

 formation of shingle, which in gales the strong breakers 

 driving against the cliff forms a ' powerful artillery 

 with which the ocean assails the bulwarks of the land,' 

 and aids in the work of destruction. On the east and 

 south of England, where the strata largely consist of 

 boulder-clay, Eocene clays, chalk, and oolitic sands, 



