Microscopical Light ifi Geological Darkness. — Clay pole. 227 
willing to allow. Here we have a supply from which it can 
be drawn as wanted without disturbing the existing balance 
of atmospheric composition, or compelling us to assume that 
in the early days of life the air was materially dififerent from 
what it is at the present time. 
I am sure it must be interesting to the working members 
of the American Microscopical Society to see how the inves- 
tigation of these minute bubbles in the crystalline rocks leads 
on to the discovery of a possible origin of the carbon in our 
coal. To any geologists present I must excuse myself for 
considering only part of the problem and saymg nothing 
of the other stores of this carbonic acid in the rocks of the 
earth compared with which the coal and other free carbon in 
the earth is a mere vanishing quantity. But the conditions 
differ and the solution of that problem must differ also. 
The imconsidered elements would, if introduced, vastly 
and unduly extend this discussion, while they would not in 
any way conflict with what I have said. They would com- 
plicate, but not invalidate the argument. I have merely 
endeavored to put forw'ard and maintain a mechanism where- 
by carbon-dioxide could be obtained as wanted by the plant- 
world without charging the atmosphere w^ith the whole 
amount at once.* I have shown how the deposit in the at- 
mospheric bank can be obtained through the receiving teller 
while the paying teller is constantly releasing it in response 
to checks on demand. 
Meanwhile I have given you a glimpse down some of the 
long vistas of geologic time. I have brought before you 
some of the processes of world making — some actual records 
of aeons long gone by — some relics of remote conditions en- 
tombed when time was young. You have in imagination, 
seen the glowing lithosphere slowly cooling and crystallizing 
and as the solid earth was built there were stored in its founda- 
tion stones these samples of its primeval atmosphere, sealed 
*An interesting possibility — I may say, from some points of view, a 
probability — would lead us too far here, if we were to attempt its discus- 
sion. But there is nothin.t^ unlikely in the supposition that the whole 
oxygen of the atmosphere has been set free from its combination in the 
form of carbon-oxide by the action of plant-life. Such a supposition is 
beset with some difficulties, not, perhaps, insuperable, but it has many 
strong reasons in its favor. 
