Microscopical Light in Geological Darkfiess. — Clay pole. 221 
sumption does not exceed 350,000,000 tons, so that one single 
cubic mile, 7,000,000,000 tons, would suffice to supply us all 
for twenty years. But the stock of coal and the like, actually 
in the ground, far exceeds, as I have said, even this enormous 
figure. To attain anything like exactness in such data is 
manifestly impossible, but we cannot assign to the world's 
store of mineral fuel, or the coal contents of our coal fields, 
oil fields and the like, a less amount than 2,000 cubic miles at 
the least, or about ten times what could be obtained from the 
air. Here lies the enigma, and, as you see, the botanist has 
not furnished any interpretation of it. 
It is easy to say, as many have said, that there vva; a larger 
supply of carbonic acid in the atmosphere then, than there 
is now. This is cutting rather than untying the Gordian knot. 
Perhaps it was so. The explanation is plausible. But the 
plausible in nature is not always or usually the true. 
Time will not allow a full discussion of this topic this even- 
ing. It must suffice to indicate, in a general way, the reasons 
which preclude us from accepting the reply as good and suffi- 
cient. 
In the first place, let us consider the demand of the geolo- 
gist. We have mentioned the coal beds, the oil and the gas, 
but these are far from being all that he requires. There are 
in the earth huge beds of black shale, holding often from 5 
to 15 per cent, of carbonaceous matter. This far exceeds 
the mass of the coal and we may safely put the figure up 
from 2,000 to 20,000 cubic miles. Alexander Winchell's 
total is nearer 30,000. Then the vast stores of peat and the 
whole animal and vegetable creation, or at least the carbon 
which they contain, must be included, and this defies exact 
calculation. Lastly, the mass of coal that has been destroyed 
by erosion must be added— small though it be beside the vast 
total. Considering all these it seems perfectly safe to set down 
the mass of unoxydised carbon in the earth's crust at 50,000 
cubic miles, or 250 times as much as that now existing in the 
air— a proportion of 10 per cent. 
Facing this fact the botani.st is scarcely willing to admit 
that plants could flourish in such a medium. Ferns and their 
allies have been grown in cases charged with an atmosphere 
containing 10 per cent, of carbonic anhydride, and possibly 
