179 
Seventh, basalt or whinstone, which consists of 
feldspar and hornblende, with materials derived 
from the decomposition of the primary rocks ; the 
crystals are generally so small as to give the rock 
a homogeneous appearance ; and it is often dis- 
posed in very regular columns, having usually five 
or six sides. 
Eighth, bituminous or common coal. 
Ninth, gypsum, the substance so well known by 
that name, which consists of sulphate of lime ; 
and often contains sand. 
Tenth, rock salt. 
Eleventh, chalk, which usually abounds in re- 
mains of marine animals, and contains horizontal 
layers of flints. 
Twelfth, plum-pudding stone, consisting of pebbles 
cemented by a ferruginous or siliceous cement. 
To describe more particularly the constituent 
parts of the different rocks and strata will be un- 
necessary ; at any time, indeed, details on this 
subject are useless, unless the specimens are 
examined by the eye ; and a close inspection and 
comparison of the different species will, in a short 
time, enable the most common observer to dis- 
tinguish them. 
The highest mountains in these islands, and 
indeed in the whole of the old continent, are con- 
stituted by granite ; and this rock has likewise 
been found at the greatest depths to which the 
industry of man has as yet been able to penetrate ; 
micaceous schist is often found immediately upon 
granite ; serpentine or marble upon micaceous 
schist : but the order in which the primary rocks 
n 2 
