114 Proceedings of the Royal Irish Academij. 



comparison for an appreciation of the wear that these coasts have 

 undergone, and consequently merit detailed citation. Under the 

 heading ^^ Destroying and Transporting Power of Currents" and sub- 

 l^eading ^^ Action of the Sea on the British Coast, Shetland Islands, 

 Sfc," he says (p. 507, vol. i.) : "The northmost group of the British 

 Isles, the Shetlands, are composed of a great variety of rocks, in- 

 cluding granite, gneiss, mica schists, serpentine, greenstones, and 

 many others, with some secondary rocks, chiefly sandstones and 

 conglomerates. These islands are exposed continually to the uncon- 

 trolled violence of the Atlantic, and no land intervenes between the 

 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 rocks, imitating the forms 

 of columns, pinnacles, and obelisks." 



(p. 509.) — "In some of the Shetland Islands, as on the west of 

 Mickle Eoe, dykes or veins of soft granite have mouldered away, while 

 the matrix in which they are enclosed, beiDg of the same substance 

 but of a firmer texture, have remained unaltered. Thus long narrow 

 ravines, sometimes 20 feet wide, are laid open, and often give access to 

 the waves." 



After describing some huge cavernous apertures, into which 

 the sea flows for 250 feet at Loeness, Dr. Hibbert, wi'iting in 

 1822, enumerates the other ravages of the ocean: "But the most 

 sublime scenes are where a mural 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, the waves having in their repeated assaults forced them- 

 selves an entrance. This breach, named the Grind of ISTaver (fig. 47) 

 is widened every winter by the overwhelming sui-ge that, finding a 

 passage through it, separates large stones from its sides, and forces them 

 to a distance of not less than 180 feet. In two or thi'ee spots the frag- 

 ments which have been detached are brought together in immense 

 heaps, that appear as an accumulation of cubical masses, the product of 

 some quarry" (Hibbert, " Description of the Shetlands." Edin., 1822). 



" There are localities in Shetland in which rocks of almost every 

 variety of mineral composition are suffering disintegi'ation. Thus the 



