218 LIGHT SCIENCE FOR LEISURE HOURS. 



destructive forces to which the land is subject than 

 promise to make up for the land which has been swept 

 away. In the first place, every part of these banks 

 consists of the debris of other coasts. Now we cannot 

 doubt that of earth which is washed away from our 

 shores, by far the larger part finds its way to the bottom 

 of the deep seas ; a small proportion only can be brought 

 (by some peculiarity in the distribution of ocean- 

 currents, or in the progress of the tidal wave) to aid in 

 the formation of shoals and banks. The larger, there- 

 fore, such shoals and banks may be, the larger must 

 be the amount of land which has been washed away 

 never to reappear. And although banks and shoals 

 of this sort grow year by year larger and larger, yet 

 (unless added to artificially) they continue always 

 either beneath the surface of the water in the case of 

 shoals, or but very slightly raised above the surface. 

 Now, if we suppose the destruction of land to proceed 

 unchecked, it is manifest that at some period, however 

 remote, the formation of shoals and banks must come 

 to an end, owing to the continual diminution of the 

 land from the demolition of which they derive their 

 substance. In the meantime, the bed of the sea 

 would be continually filling up, the level of the sea 

 would be continually rising, and thus the banks would 

 be either wholly submerged through the effect of this 

 cause alone, or they would have so slight an elevation 

 above the sea-level that they would offer little resist- 

 ance to the destructive effects of the sea, which would 

 then have no other land to act upon. 



