222 TJic American Geologist. October, i898 
so large a proportion may have been consistent with the 
existence of the cryptogams of the early eras. Botany cannot 
give an absolute denial. Experiments on this point are few 
and not very definite. Prof. Daubeny, of Oxford, stated 
nearly fifty years ago, in a paper read before the British 
Association in 1849, that ferns and their allies cannot bear 
more than 10 per cent., but could exist in an atmosphere 
containing 5 per cent, of carbon-dioxide. Prof. Boussin- 
gault reported, in 1864, that different plants flourish best in 
atmospheres ranging from 8 per cent, downward. We may 
therefor infer that the above requirement of the geologist is 
close to, if not above, the limit of tolerance of plants allied 
to those by which the mass of our coal was made, and that 
on this ground it is scarcely tenable. 
On the zoological side the evidence is also uncertain. 
Some of the lower animals, such as fishes and amphibians, 
are tolerant of a far larger amount of carbon-dioxide than 
can be endured by the higher groups. But it can scarcely 
be probable that even they could live in an atmosphere con- 
taining as much as 10 per cent. 
However, setting aside both these as inconclusive, a physi- 
cal objection remains to be considered of more serious im- 
port. By calculation we find that the conversion of this mass 
of carbon into carbon-dioxide would absorb all or nearly all 
the oxygen in the air and leave it devoid of that essential ele- 
ment. We may, therefore, safely assert that whatever the 
earth's atmosphere may have been in the very early times, the 
carbon now in the crust cannot have existed as carbonic acid 
in the atmosphere at any one time since animal life began. 
Returning, then, to our former ground we see that, with- 
out dogmatizing on the primitive atmosphere, we are unable 
to accept this plausible explanation as a good and sufficient 
solution. We cannot hypothecate a sufficient capital stock 
of carbon to meet the immense and continuous drafts that 
have been made upon it. 
So strongly did one of our most able chemical geologists, 
the late Dr. Sterry Hunt, feel this difficulty, that he was 
driven to make the suggestion that the earth had picked up the 
needed material from the space-realms during her annual and 
secular journeys — a remark which Alexander Winchell says 
