re of Ayr; this lake
receives its water from the granite hills which are at its head.
Secondly, some small lakes which receive the washings of the granite
mountain, Crifle, in East Galloway. Thirdly, Cornwall, a county in which
I have not been, but which is sufficiently known as possessing kaolin
and granite.

Another example from a very distant country we have both from M.
Pallas, in the Oural mountains, and from M. Patrin, who has given a
mineralogical _notice_ of the Douari, _Journal de physique, Mars_ 1791.
Here we find the following observation.

"Parmi les chose interessantes qu'offrent les rives de Chilea, on
remarque au dessous de la fonderie, des collines de petunt-fe blanc
comme la neige, parseme de mica argentin de la plus grande tenuite.
Dans le voisinage de ce petunt-fe est une argile micacee, qui en est
peut-etre une decomposition: on essaya en ma presence d'en faire de
la poterie qui avoit tous les caracteres du meilleurs biscuit de
porcelaine."

We have now been endeavouring to illustrate the wasting and washing
away of the solid land, in the examples of decayed rocks and water worn
stones, all of which are traceable, though at a great distance, to their
source; we are now to consider another species of substance, which is
still more particular as to the place of its production, or to its
original situation, this being only in the veins of the earth. Among all
the various productions of mineral veins, we have only now in view
some particular metallic substances which do not seem to waste and be
dissolved, as many of them are, in being long exposed to the influence
of air and rain. When, therefore, the solid parts of the land are wasted
in time, and carried away from the surface of the earth, the contents of
the veins, which are occasionally found in those decayed parts of the
land, are also carried away in the stream; but as the specific gravity
of those metallic contents is much greater than the other stony
materials moved in the stream, they sink to the bottom, and tend much
more to be deposited upon the land, than those stones which had moved
with them from their place. Hence it is, that deposits, rich in those
metallic substances, are formed in certain places of the soil; and these
are sought for, upon account of the value of their contents. Thus,
stream tin, which in the time of the Romans formed a subject of traffic,
is still found in the soil of Cornwall, even in great profusion, at this
day.