570 F. R. BARNETT 



rock and sent it tumbling down the steep slope which falls away from 

 the escarpment. 



The other hypothesis, that of lightning, seems the more probable, 

 and the writer wishes to call attention to it as an example of a kind 

 of phenomenon rather rarely noted in geological literature. A few 

 instances of the disruptive effects of lightning are on record. 



Hibbert^ describes as follows the effect of lightning on the cliffs 

 of micaceous schist on the east side of the island of Fetlar, one of the 

 Shetland Islands. 



A rock 105 feet long, 10 feet broad, and in some places more than 4 feet 

 thick, was, in an instant, torn from its bed, and broken into three large and several 

 lesser fragments. One of these, 26 feet long, 10 feet broad, and 4 feet thick, 

 simply turned over. The second, which was 28 feet long, 17 feet broad, and 5 feet 

 in thickness, was hurled across a high point of a rock to the distance of 50 yards. 

 Another broken mass, about 40 feet long, was thrown still farther but in the same 

 direction, quite into the sea. There were also many lesser fragments scattered up 

 and down. 



T. R. Dakyns, in his paper on "Modern Denudation in N. Wales,"^ says: 



During the great thunderstorm that occurred in N. Wales in the middle of 

 August, 1898, a mass of rock was broken and thrown down the Llyn Teyrn. 

 This is known to have been done by lightning, as it was not there until after the 

 storm. 



In a conversation with the writer, George Otis Smith has stated 

 that during a thunderstorm in 1904, he observed lightning strike on 

 the summit of Mt. Battle, in the northern portion of the Rockland 

 quadrangle^ (Maine), and a mass of quartzitic conglomerate several 

 feet in diameter was broken from the glaciated surface and thrown 

 out. 



While the most commonly observed effects of lightning on rocks 

 seems to be that of fusion resulting in the production of fulgurites or 

 glassy coatings,4 no evidence of fulgurites nor of glassy coatings was 

 observed either on these fragments or in the cavity from which they 

 were thrown, but since Hghtning of the disruptive type is apparently 



1 Samuel Hibbert, Description of the Shetland Islands, 1822, p. 389. For this 

 account of lightning effect Hibbert says he is indebted to Geo. Low, M. S. 0} Rev. 



2 Geological Magazine, new series, Vol. VII, 1900, No. i, p. 19. 



3 Rockland Folio No. 158, U. S. Geol. Survey, May, 1908. 



4 R. R. Julian, "A Study of the Structure of Fulgurites," Jour. Geol, Vol. IX, 

 1901, pp. 673-93. 



