508 ADDRESS OF T. STERRY HUNT. 
by the action of carbonates of magnesia and soda, remains at first 
dissolved as bicarbonate, and is only separated in a solid form, 
when in excess, or when required for the needs of living plants 
or animals; which are dependent for their supply of calcareous 
matter, on the bicarbonate of lime produced, in part by the proc- 
ess just described, and in part by the action of carbonic acid on 
insoluble lime-compounds of the earth’s solid crust. So many 
limestones are made up of calcareous organic remains, that a 
notion exists among many writers on geology that all limestones : 
are, in some way, of organic origin. At the bottom of this lies 3 
the idea of an analogy between the chemical relations of yege- 
table and animal life. As plants give rise to beds of coal, so ani- 
mals are supposed to produce limestones. In fact, however, the 
synthetic process by which the growing plant, from the elements 
of water, carbonic acid and ammonia, generates hydrocarbonace- 
ous and azotized matters, has no analogy with the assimilative 4 
process by which the growing animal appropriates alike these or- : 
ganic matters and the carbonate and phosphate of lime. Without : 
the plant, the synthesis of the hydrocarbons would not take place, 
while independently of the existence of coral or mollusk, the car- 
bonate of lime would still be generated by chemical reactions, and 
would accumulate in the waters until, these being saturated, its l 
excess would be deposited as gypsum or rock-salt are deposited. 
Hence in such waters, where, from any causes, life is excluded, 
accumulations of pure carbonate of lime may be formed. In 1861 
I called attention to the white marbles of Vermont, which occur q 
intercalated among impure and fossiliferous beds, as apparently 
examples of such a process.* 
It is by a fallacy similar to that which prevails as to the or- 
ganic origin of limestones, that Daubeny and Murchison were led 
to appeal to the absence of phosphates from certain old strata as 
evidence of the absence of organic life at the time of their accu- 
mulation.t Phosphates, like silica and iron-oxyd, were doubtless 
constituents of the primitive earth’s crust, and the production of 
apatite crystals in granitic veins, or in crystalline schists, is @ proc- 
ess as independent of life as the formation of crystals of quartz 
or of hematite. Growing plants, it is true, take up from the soil 
or the waters dissolved phosphates, which pass into the skeletons 
Booo eea a 
* Amer. Jour. Sci., II, xxxi, 402. 
t Siluria, 4th ed., pp. 28 and 537. 
