568 



SILTING UP OF ESTUAEIES. 



[Ch. XXII. 



Suffolk, which are between twenty and three hundred feet in 

 height, and which waste at various rates of from one foot to 

 six yards annually. It also bears away, in co-operation with 

 the Thames and the tides, the strata of London clay on the 

 coasts of Essex and Sheppey. The sea at the same time con- 

 sumes the chalk with its flints for many miles continuously 

 on the shores of Kent and Sussex — commits annual ravages 

 on the freshwater beds, capped by a thick covering of chalk- 

 flint gravel, in Hampshire, and continually saps the founda- 

 tions of the Portland limestone. It receives, besides, during 

 the rainy months, large supplies of pebbles, sand, and mud, 

 which numerous streams from the Grampians, Cheviots, and 

 other chains, send down to the sea. To what regions, then, is 



It is not retained in mechanical 

 suspension by the waters of the ocean, nor does it mix with 

 them in a state of chemical solution, — it is deposited some- 

 where, yet certainly not in the immediate neighbourhood of 

 our shores ; for, in that case, there would soon be a cessation 

 of the encroachment of the sea, and large tracts of low land, 

 like Eomney Marsh, would almost everywhere encircle our 

 island. 



As there is now a depth of water exceeding thirty feet, in 

 some spots where towns like Dunwich flourished but a few 

 centuries ago, it is clear that the current not only carries far 

 away the materials of the wasted cliffs, but is capable also of 

 excavating the bed of the sea to a certain moderate depth. 



all this matter consigned ? 



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in the bottom of 



Ocean. — To what extent in a downward direction this power 

 of submarine erosion extends, is a question of the highest 

 geological interest, and one respecting which we have at 

 present no very accurate information. The sea between 

 Great Britain and the Continent of Europe has rarely a 

 depth of more than 50 fathoms, and the only part which 



01 more than 50 

 exceeds 100 fathoms is a narrow channel skirting the western 



Norw 



fathoms 



Baltic, the extraordinary depth of 430 fathoms, or 2,580 feet. 

 Some hydrographers are of opinion that even this channel 

 has been scooped out by a tidal current, but to me it appears 



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