MINERALS. 
335 
mountains, has justly obtained the name of volcanic 
earth. 
The first order vve have noticed, such as the 
granite, porphyry, statuary marble, &c. from their 
being situated below the others, are supposed to 
have been formed before them, and therefore take 
the name of primitive earths . The layers above 
these are the secondary earths : after them follow 
the third series, and then the volcanic earths. 
These four kinds, either in a separate or united 
state, give figure, and various degrees of solidity, to 
the different mountains. The mountains which are 
formed of primitive layers are generally pointed. 
Those which partake of a volcanic origin are almost 
conical, whilst the mountains composed of beds of 
the second or third kind are either fiat on their 
summits, or round on all sides. 
Layers composed of the two first kinds of earth 
are often interrupted by slits or cracks, some of 
which are empty, while others are filled with stony 
or metallic substances, differing in their nature from 
the component parts of the beds through which 
they pass. These cracks by the miners are called 
veins, and are found to run in several directions, and 
with different degrees of inclination. 
Buffon remarks, that in plains, the strata, or beds 
of mineral substances, are exactly horizontal. “ It 
is in mountains only,” says this naturalist, “ that 
they are inclined to the horizon; because they have 
originally been formed by sediments deposited upon 
an inclined base. 
