268 Mr. A. Tylor on Changes of the Sea-Level effected by 



any fresh spoil, yet there are few hours when its waters are 

 unemployed in fashioning and abrading the materials already 

 acquired/' In considering the effect upon the sea-level caused 

 by sand, mud, and pebbles washed in by the breakers, it is only 

 necessary to regard those materials that may be brought in from 

 cliffs above high-water mark; for the movement of sand and 

 mud below high-water mark can produce no effect upon the sea- 

 level, because the abstraction of these materials from one part of 

 the shore is exactly balanced by their addition to some other 

 part. For instance, some of the flint-pebbles which have con- 

 tributed to the recent deposit at Landguard Point have been 

 brought along shore a great distance from their original position 

 on the cliff. These flints formed an addition to the sea-bed, 

 and tended to raise its general level by displacing an amount of 

 water equal to their bulk the moment they fell on the shore 

 below high-water mark ; and it is quite clear their subsequent 

 movements, either beneath the waves or on the beach, could pro- 

 duce no further effect upon the sea-level, the spaces they occu- 

 pied on one part of the coast being balanced by the vacancy left 

 at some other. It is also evident that the beach at Landguard 

 Point will go on extending so long as the fresh supplies of 

 shingle and sand from the north exceed the removals southward. 

 In the same manner the continued supplies of pebbles from 

 the westward enables the Chesil Bank to preserve its position. 

 As soon, however, as any disturbing causes interrupt the sup- 

 plies of new material, the sand and shingle beaches dependent 

 upon them must soon disappear ; and in fact the termination of 

 every beach wiU be at that point where the waste and abrasion 

 by breaker-action are balanced by the supply of pebbles and sand 

 drifted from other places. Although it appears clear that only 

 the detritus obtained from cliffs above high-water mark need be 

 taken into calculation, yet I regret to find that scarcely any data 

 of this kind exist, and therefore it is not possible to ascertain 

 the probable effect upon the sea-level that is being produced by 

 the detritus so derived. In the same manner the per-centage of 

 soluble salts in the water of the few large rivers of which notes 

 have been published has not been given separately from the per- 

 centage of matter in suspension, and therefore we are in igno- 

 rance of the supplies that are annually introduced into the ocean 

 from the formation of submarine deposits from materials dissolved 

 in the sea-water. When the rise in the sea-level from the effect 

 of alluvium brought in suspension by rivers was being considered, 

 I supposed that that cause alone might produce an elevation of 

 1 foot in 54,000 years ; but in order to make some allowance for 

 the similai* effects that must be produced by the introduction 

 into the ocean of materials from above high- water mai'k on coast- 



