C 585 ] 
generally, if not always, formed out of the lower 
rtrata of earth. This fituation of the rtrata may be 
not unaptly reprefented in the following manner. 
Let a number of leaves of paper, of feveral different 
forts or colours, be parted upon one another; then 
bending them up together into a ridge in the middle, 
conceive them to be reduced again to a level lurface, 
by a plane fo parting through them, as to cut off all 
the part that had been raifed ; let the middle now be 
again raifed a little, and this will be a good general 
reprefentation of moft, if not of all, large tradts of 
mountainous countries, together with the parts ad- 
jacent, throughout the whole world * *. 
44. From this formation of the earth, it will fol- 
low, that we ought to meet with the fame kinds of 
earths, ftones, and minerals, appearing at the furface, 
in long narrow flips, and lying parallel to the greateft 
rife of any long ridges of mountains ; and fo, in fadt, 
we find them. The Andes in South America, as it 
has been faid before, have a chain of volcanos, that 
extend in length above 5000 miles : thefe volcanos, 
in all probability, are all derived from the -f fame 
out of ftrata ftill lower than the reft, which, perhaps, may always 
be the cafe, where ihey have volcanos in them. [See a repre- 
fentation of this in Tab. XIII. Fig. 3 ] In other inftances, how- 
ever, it often happens, that the hills, to which thefe high lands 
ferve as a bafe, are not only formed out of the ftrata next above 
them, but they ftand, as it were, in a difh, as if they had deprefled 
the ground, on which they reft, by their weight. 
* Fig. 1. reprefents a fedlion of a fett of ftrata, lying in the 
fituation juft defcribed: the fedlion is fuppofed to be made at right 
angles to the length of the ridge, and perpendicular to the ho- 
rizon. 
f See the notes to art. 36 and 53. See alfo Fig. 3. 
rtratum. 
