BaILey. | Chemistry of Gypsum. 137 
established that in a mixture of several compounds, that which 
could form a precipitate first would first be formed, and it is 
evident here that the calcium sulphate is the most insoluble sub- 
stance that can be formed. 
Some substances are less soluble in water than others, and to 
this fact we owe many of the peculiarities of the deposits. Gyp- 
sum deposits in general, and especially those of Michigan, are 
discussed by L. L. Hubbard.” He calls attention to Ochsenius’ 
theory of the methods of deposition of these substances that are 
found in sea water. With an enclosed sea we should have one 
kind of a deposit; one in which there would be first a layer of 
the least soluble substances, as for instance, calcium carbonate, 
which would be followed by a layer perhaps of calcium sulphate, 
as that is a little more soluble, and later would come a layer of 
sodium chloride, mixed with calcium sulphate, and finally the 
‘‘bittern,’’ containing bromides and some magnesium and po- 
tassium salts, would deposit last. 
If the lake or inland sea were so situated that the water could 
flow over a bar in and out, the denser water would settle to the 
lower part of the lake and would not flow out but would gradu- 
ally concentrate and drop its load of mineral. The more solu- 
ble salts would be carried out and gypsum and salt would be 
introduced with each influx of fresh water. In fact it is then 
a matter of specific gravity. Ata specific gravity of 1.0506 to 
1.1504 the calcium carbonate would deposit. This had prob- 
ably been kept in solution by the excess of carbon dioxide, 
which has not before had a chance to escape. At a specific 
gravity of from 1.1304 to 1.22 calcium sulphate would be de- 
posited. As the specific gravity increased above this the salt 
would be precipitated, and the substances still more soluble 
last. This process is analogous to that actually employed in 
the purification of brine to make salt. In this case the brine is 
heated in one end of the tank, quite near the fire, until it de- 
posits its calcium sulphate and begins to precipitate salt, then it 
is allowed to run into the larger division of the pan, where as 
55. Geological Survey of Michigan, Vol. V, Part II, p. 9, ff, 
