88 Abstraction of Nitrogen from the Atmosphere. 
These are those masses, which-are sometimes fifty feet or more 
in thickness, but are of limited extent, and whose upper and 
lower surfaces are not parallel to each other, but are more or 
less plano-convex. The other, and more commo de, is 
in beds, or layers, where surfaces are parallel, aad usually 
of great extent, but of no great thickness. This kind rarely 
or never presents single beds ; they are, on the contrary, often 
very numerous. In some places more than fifty of them have 
been counted: Generally they alternate with slate, clay an 
sandstone and sometimes with shell limestone. Coal beds 
of this kind, furnish the facts which afford manifest proofs 
that oe plants which produced the coal grew and died 
where the coal is found. How can these alternations of 
masses ot vegetable matter, indurated mud, sand and lime- 
stone, be accounted for, if we admit not the presence of land- 
floods of fresh water, and salt water, as often as the products 
of these pieooness are exhibited ?- 
OF SALT. 
Neither salt, nor fhe elements of salt, ‘with the SReAHAON S of 
soda, are to be found in the primitive class of rocks. We 
caine obliged, in the present state of our pear g 
to suppose that it remained in solution until the geological 
period at which we find it. From the writings of European 
geologists, it is impossible to refer salt to any particular pe- 
riod. Thus the salines of Bex, of Colancolan, in the An- 
des of Pee of Cordona, and of Moutier, would place it in 
the transition class; whilst those of the Jura, of Cheshire in 
England, of Poland, and of Saltzbourg, are considered to 
be coeval with the middle secondary. ~This discordance of 
position is what we ought to suppose from theory, for, like 
coal, its stepson depended mppn local circumstances, an 
not _tendency.* One obvious cause of the 
depos has of salt, is the alternation of land and sea-water, 
conbinere great atmospherical evaporating powers, which 
is the common opinion of its mode of formation, and which 
the marly ——— Rep ears accompanying it, plainly show. 
The salt springs of western country, manifestly —- to 
entioned. All our 
suppose, that seas have 
Asi in granite, gneis, &c, 
