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 lightning, and glazed on the inside like lightning- 
tubes; in it the lightning had made cylindrical 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 26,050 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 dii-ecfion, quite into the sea. There were also many smaller 
fragments scattered up and down." 
It 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. 
