56*2 
BASALTES. 
as in Scotland and Ireland. The stone is generally 
of a blackish-gray colour, difficult to break, and 
sounding under the hammer like brass. It is of 
a prismatic shape, and generally hexangular, but 
by no means constant in this respect, as basaltic 
pillars are found with three, four, five, six, and 
seven sides. Immense numbers of these pillars are 
sometimes collected together and joined side by side, 
either in a vertical or an inclined direction. They 
vary considerably both in size and height, being 
found from a few inches to three or four feet in 
diameter, and from five to fifty or sixty feet high. 
Sir J. Banks remarked, when he visited the island 
of Staflfa, that the surfaces of the large pillars were 
in general rough, uneven, and full of cracks in all 
directions, some of which were filled with a yellow 
spar. He likewise noticed that the surfaces of the 
larger number were concave, though some were evi- 
dently convex. 
When a large mass of basaltes is found to ex- 
tend to a considerable distance with a tolerably uni- 
form surface, it is called a causeway. In France 
there are several basaltic causeways, particularly in 
Auvergne, in Velay, and Vivarais ; but none of 
these are to compare with the Giant’s Causeway on 
the northern coast of Ireland. This wonderful as- 
semblage of basaltic columns has been frequently 
described by travellers; but the most recent account 
is that by M. Pictet, who was in Ireland in the 
year 1801 . This gentleman describes it as a sort of 
promontory, or rather pier, gradually descending 
