ORIGIN OF CRYSTALLINE ROCKS. 501 
ification. The whole history of these rocks, moreover, shows that 
their various alternating strata were deposited, not as precipi- 
tates from a seething solution, but under conditions of sedimen- 
tation very like those of more recent times. In the oldest known 
of them, the Laurentian system, great limestone formations are 
interstratified with gneisses, quartzites and even with conglom- 
erates. All analogy, moreover, leads us to conclude that even at 
this early period, life existed at the surface of the planet. Great 
accumulations of iron-oxyd, beds of metallic sulphids and of 
graphite, exist in these oldest strata, and we know of no other 
meee seo that of organic matter, capable of generating these 
produe 
cans had already arrived at the conclusion, which in the 
present state of our knowledge seems inevitable, that “all the car- 
bon yet known to occur in a free state, can only be regarded as 
a product of the decomposition of carbonic acid, and as derived 
from the vegetable kingdom.” He farther adds, ‘‘living plants 
decompose carbonic acid; dead organic matters decompose sul- 
phates, so that, like carbon, sulphur appears to owe its existence 
in a free state to the organic kingdom.”* As a decomposition 
(deoxidation) of sulphates is necessary to the production of me- 
tallic sulphids, the presence of the latter, not less than that of 
free sulphur and free carbon, depends on organic bodies; the part 
which these play in reducing and rendering soluble the peroxyd of 
iron, and in the production of iron ores is, moreover, well known. 
It was, therefore, that, after a careful study of these ancient rocks, 
I declared in May, 1858, that a great mass of evidence ‘ points 
to the existence of organic life, even during the Laurentian or so- 
called azoic period.” + 
This prediction was soon verified in the discovery of the Eozoon 
Canadense, of Dawson, the organic character of which is now ad- 
mitted by all zoologists and geologists of authority. But with 
this discovery, appeared another fact, which afforded a signal veri- 
fication of my theory as to the origin and mode of deposition of 
serpentine and pyroxene. The microscopic and chemical re- 
searches of Dawson and myself showed that the calcareous skel- 
eton of this foraminiferal organism was filled with the one or the 
other of these silicates in such a manner as to make it evident that 
* Bischof, Jaen, lst. ed., Il, 95. English ed., I, 252, 344. 
ur. Science, II, xxv, 436. 
