Relations of the Atmosphere. 353 
While some have imagined an inorganic origin to the carbon 
found in the form of graphite, and even to petroleum and to 
coal, sound reasoning is, we think, on the side of those who, start- 
ing from the conception of an originally oxidized globe; see no 
evidence of any process of deoxidation therein which does not, 
directly or indirectly, depend upon vegetable life, and hence 
assign an organic origin to all carbons and hydro-carbons, 
When we take into account the vast amounts of these, from the 
graphite of Eozoic times to the coals, lignites and petroleums 
of the Tertiary, we can scarcely doubt that the total amount 
of carbon which has been reduced from carbonic dioxide is 
equal to many times the equivalent of the oxygen now present 
in the atmosphere. Whether the great excess of oxygen thus 
liberated may perhaps have been absorbed in the production 
is ferric oxide, as above indicated, is a part of the problem be- 
ore us. 
It may here be noted that in addition to the fossil carbon- 
aceous bodies already mentioned, the rocky strata of the 
earth include great thicknesses of pyroschists, which are argilla- 
ceous sediments more or less impregnated with hydro-carbon- 
aceous matters allied to coal in composition. ‘To give a single 
example, Newberry estimates the proportion of such matters 
diffused through the 300 or 400 feet of Devonian black shales 
which underlie the eastern half of Ohio, to equal fifteen per 
cent, and to be equivalent to a layer of coal fifty feet in thick- 
ness over the whole area.* 
In this connection it must be considered that the chemical 
composition of the various hydrocarbonaceous fossil substances 
implies a deoxidation not only of carbonic dioxide but of wa- 
ter. The amount of liberated oxygen from the latter would 
equal, for the different coals and asphalts, from one-eighth to 
one-fourth, and for the petroleums, one-half of that set free in 
the deoxidation of the carbon which these hydrocarbonaceous 
ies contain. 
and the magnesian carbonate set free in like manner fr 
Magnesian silicates, must decompose the chlorid of calcium 
contained in the primitive ocean, thereby giving rise to 
alkaline and magnesian chlorides on the one hand, and to 
Carbonate of lime on the other, is a consequence which seems 
to have escaped Ebelmen, and was pointed out by the present 
* Geology of Ohio, vol. i, page 162. 
