These two species are, _first_, granite regular in its composition, or
stratified in its construction; and, _secondly_, granite in mass, or
irregular in its construction. Let us now endeavour to make use of these
generalizations and distinctions.
In examining the great diversity of our whinstone, trap, or basaltes, it
is found at last to granulate into granite; at the same time those two
different species of rock-stone may be distinguished. A perfect granite
has not in its composition necessarily any argillaceous earth, farther
than may be in the natural constitution of its distinct parts; whereas,
a perfect basalt may have abundance of this substance, without any
quartz or any siliceous body. A perfect granite, is, therefore, an
extremely hard stone, having quartz and feldspar for its basis; but a
perfect whin or basaltes may be extremely soft, so as to cut easily with
a knife. In like manner granite is a composition which graduates into
porphyry; but porphyry is only whinstone of a harder species. Therefore,
though perfectly distinct, those three things graduate into each other,
and may be considered as the same.
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