[October, 
462 The Atmosphere Considered 
distribution are very fairly accounted for. I shall show 
presently that there are other grounds for the supposition 
that the carbonic acid is now much less than it has been 
in these far back periods; nor is it to be considered that it 
reached its maximum even in the Carboniferous age. It is 
true that the earlier formations afford nothing like such a 
superabundance of fossil plants ; but this has been well 
accounted for by Dr. Sterry Hunt. He has shown that the 
vast amount of chemical acftion that has taken place in the 
reduction and accumulation of the metalliferous deposits of 
the older Palseozoic rocks will readily account for the scarcity 
of fossil vegetation in those rocks. To the decay of plants 
and the reducing aCticn of the resulting carbonic acid those 
deposits must be in great measure attributed; and their 
existence proves that an abundant flora flourished. The 
manner in which this chemical aCtion takes place will be 
explained further on. I shall just quote Dr. Hunt’s words 
on this point : — “ Where are the evidences of the organic 
material which was required to produce the vast beds of 
iron-ore found in the ancient crystalline rocks. I answer 
that the organic matter was, in most cases, entirely con- 
sumed in producing these great results, and that it was the 
large proportion of iron diffused in the soils and waters of 
these early times which not only rendered possible the 
accumulation of such great beds of ore, but oxidised and 
destroyed the organic matters which in later ages appear in 
coals, lignites, pyroschists, and bitumens. Some of the 
carbon of these early times is, however, still preserved as 
graphite, and it would be possible to calculate how much 
carbonaceous material was consumed in the formation of 
the great iron-ore beds of the older rocks, and to determine 
of how much coal or lignite they are the equivalents.”* 
If we also refledb that the enormous quantities of lime- 
stones which are found in the older formations have been 
largely dependent on the carbonic acid of 'the atmosphere — ■ 
in effect, the further we retrograde towards a primitive con- 
dition of things the more diredtly such carbonic acid must 
have come into requisition for such purposes, as there would 
be the less of it stored up in rocks, to be re-utilised as at the 
present day, when much of the carbonate of lime in waters 
is obtained by the disintegration of pre-existing limestones 
— and remember also the carbon that was required for the 
teeming animal life of ancient times, we shall see that there 
* “On the Origin of Metalliferous Deposits.” — Chem. and Geological 
Essays, p. 229. 
