The
next modification to be distinguished in mineral bodies is that of
gravel; and this differs in no respect from sand, except in point of
size. Next after gravel, in the order of ascent, come stones; and these
bear nearly the same relation to gravel as gravel does to sand. Now,
by stones is to be understood the fragments of rocks or solid mineral
bodies; and there is a perfect gradation from those stones to sand.
I have already endeavoured to explain the formation of those stony
substances; and now I am treating of a certain system of circulation,
which is to be found among minerals.
M. de Luc censures me for not giving the origin of sand, of which I form
the strata of the earth. He seems to have misunderstood my treatise. I
do not pretend, as he does in his theory, to describe the beginning of
things; I take things such as I find them at present, and from these
I reason with regard to that which must have been. When, from a thing
which is well known, we explain another which is less so, we then
investigate nature; but when we imagine things without a pattern or
example in nature, then, instead of natural history, we write only
fable.
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