45 6 
The Atmosphere Considered 
[October, 
XL THE ATMOSPHERE CONSIDERED IN ITS 
GEOLOGICAL RELATIONS. 
By Edward T. Hardman, F.C.S., 
H.M. Geological Survey of Ireland. 
t HE gaseous envelope which surrounds our globe plays 
a very considerable part in the chemical changes ever 
^ going on in rock formations, whether actually at the 
surface — as in what is called the “weathering” of rocks — 
or in the less apparent, but perhaps more powerful, aCtion 
carried on at greater depths whither the atmospheric gases 
are conveyed by the aCtion of percolating water. It has 
been shown, by the experiments of Prof. Rogers,* as well 
as by those of Bischof t and others, that perfectly pure 
water has a very appreciable solvent effect on rocks and 
minerals ; and that power is immensely augmented, and 
capability to produce even more momentous alterations in 
the form of chemical decomposition added, when it is 
charged with carbonic acid, oxygen, nitric acid, and other 
matters derived direCtly or indiretbly from the atmosphere. 
While, on the one hand, the influence of the atmosphere 
disintegrates and destroys rock-masses, on the other it is 
mighty in building them up. Without the small percentage 
of carbonic acid contained in air — a quantity relatively mi- 
nute, but in the aggregate enormous — there could be no 
vegetation. The vegetable kingdom, which obtains its sup- 
plies of carbon from those insignificant traces, would be 
wanting, and there could be none of the coal-beds which 
form such important members of our rock-formations. This 
is a direCt and palpable case. But if we consider the im- 
mense masses of limestones which have been accumulated 
from those of the Laurentian period, and for aught we know 
before it, up to the coral reefs of the present day, and which 
must owe their being indirectly to carbonic acid of former 
atmospheres, we shall have some idea of the stupendous 
results attained by very small means, provided time enough 
be granted. 
A drop of rain water absorbs a trace of carbonic acid 
from the atmosphere, falls on a rock containing lime in some 
* Report Brit. Assoc., ,1849. Trans, of Sections, p. 40. 
f Elements of Chem. Geol., English ed., vol. i. pp. 57, 58. 
