and the formation of Gypsum and Magnesian Rocks. 379 
portion of its carbonic acid by evaporation, reacts in a similar 
manner with a solution of sulphate of lime (§ 5, § 23). In this 
way, an influx of sea-water into the basin from which gypsum, 
and perhaps a portion of magnesian carbonate has already been 
deposited, would give rise to a precipitate of carbonate of lime, 
like the tufaceous limestones, whose occurrence with gypsum 
and dolomites has been already noticed. In basins which, like 
the salt lagoons of Bessarabia on the shores of the Black 
receive occasional additions of sea-water, and deposit every sum~- 
mer large amounts of salt, (Bischof, Lehrbuch, ii, 1717,) the influx 
of waters containing bicarbonate of lime would give rise to the 
formation of beds of gypsum, alternating with dolomites or 
Magnesian marls and rock salt. 
_ 67. We have already referred to the analyses of certain rivers, 
in which the sulphates are more abundant than the chlorids. 
Thus, in the Rhine, near Bonn, according to Bischof, we have 
for 100,000 parts of the water, 17-08 of solid matters, of which 
1:23 are sulphate of lime, 1°81 sulphate of magnesia, with only 
1:45 of chlorid and 8°37 of carbonate of lime; in the Danube 
hear Vienna, the predominance of sulphates is still more marked. 
The waters of the Arve, in the month of February, gave to Tin- 
gry, for 100,000 parts, 24°5 of solid matters, of which 65 were 
sulphate of lime, 6°2 sulphate of magnesia, and 8°3 carbonate of 
lime, with only 1:5 of chlorids. Now, as in river waters there 
's always pres 
of lime and sulphate of magnesia in solution are mutually de- 
composed, these waters, which are to be regarded as solutions of 
Sulphate of lime and bicarbonate of magnesia, (§ 18) w by 
their evaporation, yield gypsum and m rbonati : 
Would appear as portions of a fresh-water formation, like those 
of Aix and Auvergne. : 
The decomposition of soluble sulphates by bicarbonates of 
baryta and strontia, will explain the formation of heavy spar and 
Celestine, and their frequent association with gypsiferous roc 
68. As to the native sulphur which is often associated both 
With epigenic and sedimentary ums, it has doubtless in 
very case been formed as Hiexick long since indicated, by the 
