THE USEFULNESS OF EARTHQUAKES. 237 



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 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 

 five feet one inch thick, was dislodged from its bed, 

 and carried to a distance of from eighty to ninety 

 feet." In other parts of the Shetland Isles, where the 

 sea has encountered less solid materials, the work of 

 destruction has proceeded yet more effectively. In 

 Roeness, for example, the sea has wrought its way 

 so fiercely, that a large cavernous aperture 250 feet 

 long has been hollowed out. " But the most sublime 

 scene," says Dr. Hibbert, " is where a rnural pile of 

 porphyry, escaping the process of disintegration that 

 is devastating the coast, appears to have been left as 

 a sort of rampart against the inroads of the ocean. 

 The Atlantic, when provoked by wintry gales, batters 

 against it with all the force of real artillery ; and the 

 waves, in their repeated assaults, have at length forced 

 for themselves an entrance. This breach, named the 



