OF THE SEA AND LAND. 43 



-by rivers is deposited at their entrances, much also is 

 moved to greater distances, by the influence of tides and 

 currents. This takes place principally with the lighter 

 materials, the finer sand and mud; while the work of 

 the waves is to pulverize the coarser deposits, which 

 would otherwise so accumulate as to encumber every sea 

 shore. Losing much of their specific gravity by im- 

 mersion, and rendered further buoyant by the increased 

 ratio of their surfaces to their bulks, these become very 

 moveable ; while their facility of transportation is in- 

 creased by the declivity of the bottom, on which they 

 necessarily tend to the point of rest. And that these 

 materials do thus travel to great distances from the land, 

 we know from soundings ; which, except in occasional 

 rocky ground, always bring up clay, sand, and fragments 

 of rock ; while, if we cannot ascertain their depths, the 

 penetration of the lead-line through them has has often 

 been known to exceed twelve feet. If the Dogger Bank 

 is entirely composed of such materials, their depth, in 

 this case, is ascertained to reach to nearly eighty feet. 

 But our imperfect means of examination do not compel 

 us to limit the range of either depth or extent. We know 

 not where the distribution can cease ; while, even to 

 twelve feet, time may add an indefinite depth. In the 

 shallower seas, the effects are far more within the reach 

 of examination ; and thus it has been computed that 

 the Baltic shoals at the rate of forty inches in a cen- 

 tury, an effect, however, of which the true cause is 

 disputed, and that in the Yellow Sea of China, the 

 process is so rapid as to allow a time to be fixed for its 

 filling up. But, the data are rarely sufficient for such 

 conclusions : since the continued transference of the 

 materials renders it impossible to depend on distant 

 inferences from given soundings. Sand-banks consti- 

 tute the obvious proof of the power of the sea in trans- 



