200 THE GEOLOGIST. 



in Mexico, upwards of 15,000 feet in height, Humboldt noticed the 

 electric effect of lightning. He brought away pieces of a mass of 

 trachyte pierced by hghtning, and glazed on the inside like lightning- 

 tubes; in it the hghtning had made cyhndrical tubes three inches 

 long, in such a manner that the upper and lower openings could be 

 distinguished apart, the rock surrounding these openings being also 

 vitrified. Arago refers to the vitrification of rock (without tubes), 

 which has been seen at a vertical height of 26,650 feet, over an ex- 

 tensive surface, at the Lesser Ararat and other places.* I possess a 

 specimen of rock from Canada, which (being at the present time mis- 

 laid, I cannot therefore say positively what it is, but I believe it to 

 be syenite) is thus covered on its exposed surface by a distinct coating 

 of enamel. Several well-attested facts have been collected by Arago, 

 showing the actual vitrification of stones, bricks, and other bodies, by 

 lightning. 



To illustrate the immense power of lightning, in splitting and 

 moving large masses of rock, I may be permitted to give the following 

 quotation from the MSS. of the Eev. George Low, of Fetlar, in Hib- 

 bert's " Shetland Islands :" — 



" At Funzie, in Fetlar, about the middle of the last century, a rock 

 of mica-schist, 105 feet long, 10 feet broad, and in some places 4 feet 

 thick, was in an instant torn by a flash of lightning from its bed, and 

 broken into three large and several small fragments. One of these, 

 26 feet long, 10 feet broad, and 4 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 a 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." 



Tt is in loose sand that we meet with the silicified tubes produced 

 by lightning in the greatest abundance. Almost any substance is 

 liable to be melted that contains even the smallest portion of silex. 



My friend. Dr. Bigsby, informs me he has seen, many years ago, 

 what he believes to be the effects of lightning in the chalk near 

 Carisbrook, Isle of Wight. These consisted of tubes, perpendicular to 



* Humboldt's Cosmos, vol. i. and vol. iv. 



