230 LIGHT SCIENCE FOR LEISURE HOURS. 



must necessarily be a slow one ; in fact, many may 

 be disposed to say that it is certainly a slow process, 

 since we see that it does not alter the forms of conti- 

 nents and islands perceptibly in long intervals of time. 

 But, as a matter of fact, we have never had an oppor- 

 tunity of estimating the full effects of this cause, since 

 its action is continually being checked by the restora- 

 tive forces we shall presently have to consider. Were 

 it not thus checked, there can be little doubt that its 

 effects would be cumulative ; for the longer the process 

 continued that is, the more the land was beaten 

 away the higher would the sea rise, and the greater 

 power would it have to effect the destruction of the 

 remaining land. 



We proceed to give a few instances of the sea's 

 power of effecting the rapid destruction of the land 

 when nothing happens to interfere with the local 

 action premising, that this effect is altogether insig- 

 nificant in comparison with that which would take 

 place, even in that particular spot, if the sea's action 

 were everywhere left unchecked. 



The Shetland Isles are composed of substances 

 which seem, of all others, best fitted to resist the 

 disintegrating forces of the sea namely, granite, 

 gneiss, mica-slate, serpentine, greenstone, and many 

 other forms of rock ; yet, exposed as these islands are 

 to the uncontrolled violence of the Atlantic Ocean, 

 they are undergoing a process of destruction which, 



