2l6 LIGHT SCIENCE FOR LEISURE HOURS. 



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, 

 even within historical times, has produced very note- 

 worthy changes. ( Steep cliffs are hollowed out,' says 

 Sir Charles Lyell, f into deep caves and lofty arches ; 

 and almost every promontory ends in a cluster of 

 rocks, imitating the forms of columns, pinnacles, and 

 obelisks.' Speaking of one of the islands of this 

 group, Dr. Hibbert says : f The isle of Stenness pre- 

 sents a scene of unequalled desolation. In stormy 

 winters, large blocks of stone are overturned, or are 

 removed from their native beds, and hurried to a 

 distance almost incredible. In the winter of 1802, a 

 tabular mass, eight feet two inches by seven feet, and 



