DEPOSIT OF SEDIMENT. 469 



yet certainly not in the immediate neighbour- 

 hood 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."* 



The sediment producing the line of disco- 

 loration to which we have alluded is extremely 

 fine. If a quantity of the water were removed 

 and allowed to stand for a time, it would be 

 found precipitated at the bottom as a fine 

 smooth mud. But the time occupied in its 

 subsidence is very considerable. The practical 

 chemist, whose business it is to prepare various 

 compounds, by precipitating them from a state 

 of solution, well knows how long and tedious 

 is this process. If we take a tumbler full of 

 lime-water and pour into it a little solution of 

 carbonic acid gas, the liquid will become turbid 

 and white as milk, from the formation of an 

 impalpable powder, but we must wait hours 

 before this powder becomes deposited at the 

 bottom. In like manner, doubtless, a period 

 of many hours is occupied in the precipitation 

 of the fine powder, consisting of the waste of 

 the cliffs and coast. During this time the tide 



O 



has receded, bearing its turbid water with it, 



and currents of various kinds then sweep away 



* Lyell ; " Principles of Geology," Book II., p. 108. 



