SALT. 
435 
or from the melting of the snow with which this 
immense plain is covered all the winter. Towards 
the end of summer, all the lakes as well as the 
ponds are dry, and covered at the bottom with a 
crust of salt several inches in thickness. In some 
the salt is pure, in others there is Epsom salt, (or 
sulphate of magnesia,) and several exhibit a mixture 
of both salts. Patrin remarks that the lakes which 
furnish the marine salt have a good sand for a lining, 
and that those which produce the Epsom salt have 
very stinking bottoms. “ We can hardly suppose,” 
says this naturalist, “ that these lakes are fed by 
saline springs, since there is not a stratum of salt in 
the river sediment; and it will be difficult to prove 
that the springs come from elsewhere ; for how is it 
possible they should pass under the two deep rivers 
which enclose the desert ?” 
The circumstances which accompany the differ- 
ent situations of marine salt, either in a fluid or a 
solid state, exhibit to the geologist peculiarities that 
are deserving of his notice. 
Saline springs are almost always in the neigh- 
bourhood of clay, and they frequently exist in 
countries where rocks of salt are unknown. They 
also contain other salts, chiefly gypsum and sul- 
phate of soda, or Glauber’s salt; it must likewise be 
remarked, that after great rains the springs not only 
increase in quantity, but also become more strongly 
impregnated with salt; from whence we may be 
allowed to suppose that the salt is generally formed 
in the earth from whence the water issues. Again, 
2 f 2 
