58. If we then take a rock of intermediate composition, such as that
prevailing in the Peak of Teneriffe, which Abich calls Trachyte-dolerite, its
proportion of silica being intermediate, or 58 per cent, it weighs 2.78, or more
than trachyte, and less than basalt. (Dr. Daubeny on Volcanoes second edition
pages 14, 15.)
BASALT.
The different varieties of this rock are distinguished by the names of basalts,
anamezites, and dolerites, names which, however, only denote differences in
texture without implying any difference in mineral or chemical composition: the
term BASALT being used only when the rock is compact, amorphous, and often semi-
vitreous in texture, and when it breaks with a perfect conchoidal fracture;
when, however, it is uniformly crystalline in appearance, yet very close-
grained, the name ANAMESITE (from anamesos, intermediate) is employed, but if
the rock be so coarsely crystallised that its different mineral constituents can
be easily recognised by the eye, it is called DOLERITE (from doleros,
deceitful), in allusion to the difficulty of distinguishing it from some of the
rocks known as Plutonic.
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