a897.] Fossils and Fossilization. 285 
FOSSILS AND FOSSILIZATION. . 
By L. P. Gratacap. 
(Continued from page 199.) 
There are many facts in chemistry which show that there 
can be mutual displacements in solutions of various substances, 
although there is also a series of facts that prove the additional 
solubility of insoluble salts in the presence of other salts or in 
dilute solutions. Thus, when certain salts, dissolved in asmall 
quantity of water decompose one another by double interchange 
of bases and acids, producing a precipitate of a difficultly solu- 
ble salt, no precipitate occurs in more dilute solutions, although 
the quantity of water present would not be sufficient to hold in 
solution the less soluble salt, which may be produced by the 
decomposition, if it existed in the separate state. For example, 
sulphate of lime requires about 400 parts of water to dissolve 
it; but chloride of calcium, dissolved in about 200 parts of 
water, gives no precipitate with sulphate of potash. It is sup- 
posed that the formation of sulphate of lime takes place, but 
that the presence of the chloride of potassium, which is formed 
at the same time, renders it more soluble than it otherwise 
would be. Carbonate of lime seems to be rendered more solu- 
ble by the presence of sulphate of potash and chloride of potas- 
sium. (Ludwig Gmelin, Hand-book of Chemistry.) 
On the other hand we know of the actual displacement of 
chlorides from solution by other chlorides, as the solubility of 
chloride of sodium in water diminishes, the greater the amount 
of chloride of magnesium therein dissolved. Sulphates also 
affect the relative solubility of the chlorides of sodium and 
magnesium. In regard to the assumption made here, that 
silica is driven out as carbonate of lime enters into solution, 
assuming the structural position of the dissolved carbonate, 
Bischof says, in his Chemical and Physical Geology (Cavendish 
Society, Vol. I, p. 199), that “ although silica is separated di- 
rectly from sea water by organic agency, still this separation 
