As the denominations I make use of may appear obscure or equivocal, it is necessary to explain them. By the term _clay_, I mean not only the white and yellow, but also blue, soft, hard, foliated, and other clays, which I look on as the scoria of glass, or as decomposed glass. By the word _sand_ I always understand vitrifiable sand; and not only comprehend under this denomination the fine sand which produces freestone, and which I look upon as powdered glass, or rather pumice stone, but also the sand which proceeds from the freestone destroyed by friction, and also the larger sand, as small gravel, which proceeds from the granate and rock-stone, and is sharp, angular, red, and commonly found in the bed of rivers or rivulets that derive their waters immediately from the higher mountains, or hills composed of stone or granate. The river Armanson conveys a great quantity of this sand; it is large and brittle, and in fact is only fragments of rock-stone, as calcinable gravel is of freestone. _Rock-stone_ and _granate_ are one and the same substance, but I have used both denominations, because there are many persons who make two different species of them. It is the same with respect to flints and free-stone in large pieces; I look on them as kinds of granate, and I call them _large flints_, because they are disposed like calcinable stone in strata, and to distinguish them from the flints and free-stone in small masses, and the round flints which have no regular quarries, and whose beds have a certain extent; these are of a modern formation, and have not the same origin as the flints and free-stone in large lumps, which are disposed in regular strata.