214 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. 



I 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 insignificant in 

 comparison with that which would take place, even in 

 that particular spot, if the sea's action were everyivhere 

 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, * 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 : ' The isle of Stennes 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 



