The great quantities of flint sand whether formed in mountains or in the
sea would appear to derive its acid from the new world, as it is found
above the strata of lime-stone and granite which constitute the old
world, and as the earthy basis of flint is probably calcareous, a great
part of it seems to be produced by a conjunction of the new and old
world; the recrements of air-breathing animals and vegetables probably
afford the acid, and the shells of marine animals the earthy basis,
while another part may have derived its calcareous part also from the
decomposition of vegetable and animal bodies.

The same mode of reasoning seems applicable to the siliceous stones
under various names, as amethyst, onyx, agate, mochoe, opal, &c. which
do not seem to have undergone any process from volcanic fires, and as
these stones only differ from flint by a greater or less admixture of
argillaceous and calcareous earths. The different proportions of which
in each kind of stone may be seen in Mr. Kirwan's valuable Elements of
Mineralogy. See additional notes, No. XIX.]

[_Living diamonds blaze_. l. 228. Sir Isaac Newton having observed the
great power of refracting light, which the diamond possesses above all
other crystallized or vitreous matter, conjectured that it was an
inflammable body in some manner congealed. Insomuch that all the light
is reflected which falls on any of its interior surfaces at a greater
angle of incidence than 241/2 degrees; whereas an artificial gem of
glass does not reflect any light from its hinder surface, unless that
surface is inclined in an angle of 41 degrees. Hence the diamond
reflects half as much more light as a factitious gem in similar
circumstances; to which must be added its great transparency, and the
excellent polish it is capable of. The diamond had nevertheless been