220 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, 

 therefore, 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 diminu- 

 tion 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 either be 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 

 resistance to the destructive effects of the sea, which 

 would now have no other land to act upon. 



