510 
ELEMENTS OF GEOLOGY, 
rite in India may have had a similar origin. In India, how¬ 
ever, especially in the Deccan, the term laterite ” seems to 
have been used too vaguely to answer the above definition. 
The vegetable soil in the gardens of the suburbs of Catania 
which was overflowed by the lava of 1669 was turned or 
burnt into a layer of red brick-colored stone, or in other 
words, into laterite, which may now be seen supporting the 
old lava-current. 
Columnar and Globular Structure. —One of the characteris¬ 
tic forms of volcanic rocks, especially of basalt, is the colum¬ 
nar, where large masses are divided into regular prisms, 
sometimes easily separable, but in other cases adhering firm¬ 
ly together. The columns vary, in the number of angles, 
from three to twelve ; but they have most commonly from 
five to seven sides. They are often divided transversely, at 
nearly equal distances, like the joints in a vertebral column, 
as in the Giant’s Causeway, in Ireland. They vary exceed¬ 
ingly in respect to length and diameter. Dr. MacCulloch 
mentions some in Skye which are about 400 feet long; oth¬ 
ers, in Morven, not exceeding an inch. In regard to diame¬ 
ter, those of Ailsa measure nine feet, and those of Morven an 
inch or less.* They are usually straight, but sometimes 
curved; and examples of both these occur in the island of 
StafiTa. In a horizontal bed or sheet of trap the columns are 
vertical; in a vertical dike they are horizontal. 
It being assumed that columnar trap has consolidated 
from a fluid state, the prisms are said to be always at right 
angles to the cooling surfaces. If these surfaces, therefore, 
instead of being either perpendicular or horizontal, are 
Fig. 5S8. 
Lava of La Coupe d’Ayzac, near Antraigue, io the Department of Ardeche. 
curved, the columns ought to be inclined at every angle to 
the horizon; and there is a beautiful exemplification of this 
phenomenon in one of the valleys of the Vivarais, a mount- 
* MacCul. Syst. of Geol., vol. ii., p, 137. 
