188 7. S. Hunt on the Chemistry of Natural Waters. 
geological periods will show that it must have contained a much 
larger quantity of lime-salts than at present. The alkaline car — 
bonates, whose origin has been described in § 18, and which — 
from the earliest times have been flowing into the sea, have 
gradually modified the composition of its waters, separating the 
lime as carbonate, and thus replacing the chlorid of calcium by — 
chlorid of sodium, as I have long since pointed out.” This re 
action has doubtless been the source of all the carbonate of lime 
in the earth’s crust, if we except that derived from the decom 
sition of calcareous silicates. ($12). In this decomposition 
y carbonate of soda, as already described in § 18, it results 
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elsewhere described, may intervene.* The addition of 98% 
tion of beeoeasyen of lime to such a solution gives rise, a 
magnesia. The former being much the less soluble salt, es 
ina sronaly saline liquid, is deposited as gypsum 
water both the Sulphuric acid and the magnesia, 
permanent addition to it of any foreign element. 
_* Canadian Journal for 185 9; thi 102, 
Rendus, June 9, 1864, p. ine The Jouens xxviil 
