CH. xx i 



DRIFTING OF LAEGE MASSES OF ROCK. 



503 



some 





glomerate. These islands are exposed continually to the 

 uncontrolled violence of the Atlantic, for no land intervenes 

 between their western shores and America. The prevalence, 

 therefore, of strong westerly gales, causes the waves to be 

 sometimes driven with irresistible force upon the coast, while 

 there is also a current setting from the north. The spray of 

 the sea aids the decomposition of the rocks, and prepares them 

 to be breached by the mechanical force of the waves. Steep 

 cliffs are hollowed out into deep caves and lofty arches ; and 

 almost every promontory ends in a cluster of rock, imitating 



columns 



•Modern 



Drifting of large masses of rock — 

 that the reduction of continuous tracts to such liisuJai 

 is a process in which nature is still actively engaged. 



masses 

 'The 



Hibb 

 •my 



quailed desolation. In sto „ , 



are overturned, or are removed from their native beds, and 



hurried up a slight acclivity to a distance almost incredible. 



mass 



inches by seven feet, and five feet one inch thick, was dis- 



.~™ ^om 



bed, 



removed 



a distance of from 



eighty to ninety feet. I measured the recent bed from 

 which a block had been carried away the preceding winter 

 (ad 1818), and found it to be seventeen feet and a half by 

 seven feet, and the depth two feet eight inches. The removed 

 mass had been borne to a distance of thirty feet, when it was 

 shivered into thirteen or more lesser fragments, some of which 

 were carried still farther, from 30 to 120 feet. A block, nine 

 feet two inches by six feet and a half, and four feet thick, was 

 hurried up the acclivity to a distance of 510 feet.'* 



At Northmavine, also, angular blocks of stone have been 



• "I 11 1 • I 1^ __ J_ I~ ,-x 



similai 



waves of the sea, some of which are represented in the an- 



nexed figure 39. . 



Effects of lightning.- -In addition to numerous examples oi 

 masses detached and driven by the waves, tides, and currents 



* Description of Shetland Isles, p. 

 527. Edin. 1822, to which work I am 



indebted for the following representa 

 tions of rocks in the Shetland Isles. 



