FREEZING. — LIGHTNING. 



153 



Perhaps there are no rocks which are more rap- 

 idly decomposed by the agency of frost than quartz 

 and trap rocks. These often form perpendicular 

 eminences, and, from their fissile texture, are easily 

 split into layers. The water, collecting in these 

 crevices, expands by freezing, and thus forces the 

 rock into fragments, which fall apart on the melt- 

 ing of the ice, and accumulate at the base of the 

 cliffs from which they have been precipitated, where 

 again they are acted upon by the same cause, until 

 they are reduced to minute particles. Vast accu- 

 mulations from this cause may be seen at the base 

 of East and West Rock, New-Haven ; of the Pal- 

 isades, on the Hudson ; and at Monument Mount- 

 ain, in Stockbridge, Mass. ; and, indeed, wherever 

 precipitous ledges of rocks are to be found.* 



There is one agent concerned in the destruction 

 of rocks to which we have not alluded, and that is 

 lightning. That rocks are splintered into fragments 

 by this cause, there can be no question, for numer- 

 ous instances of this kind have been recorded. Mr. 

 Lyell states that " at Funzie, in Fetlar, about the 

 middle of the last century, a rock of mica slate 105 

 feet long, 10 feet broad, and in some places four 

 feet thick, was in an instant torn by a flash of light- 

 ning from its bed, and broken into three large, and 

 several smaller fragments. One of these, 26 feet 

 long, 10 feet broad, and four feet thick, was simply 

 turned over. The second, which was 28 feet long, 

 17 broad, and 5 feet in thickness, was hurled across 

 a high point 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 smaller fragments scattered 

 up and down." 



* Higgins states that the stone ot which the colleges at Ox- 

 ford are built, is one particularly affected by frost ; and the con- 

 sequence has been the almost entire destruction of the archi- 

 tectural beauty of those once elegant buildings. 



