546 T. C. CHAMBERLIN 
first they appeared to have no relationship. This chain led on 
and on until it became connected with many of the most funda- 
mental problems of geology. When once an inquiry into the 
history of the atmosphere and its possible functions in the past 
was raised, there seemed no resting place until the origin of the 
atmosphere — and with it the origin of the earth — was reached. 
The inquiry raised profound skepticism regarding some of the 
most firmly accepted doctrines of the original state of the 
earth, its internal constitution, and the great dynamic forces 
that have controlled the larger phases of its history. A series 
of new, or partially new, hypotheses relative to these fundamental 
phenomena seemed to be necessary to fill out the group of 
alternative theories requisite to cover the ground of legitimate 
doubt based on specific reasons for doubt. In other papers I 
have given a partial expression to the hypotheses framed to 
cover these points.* The exposition of these has not in all cases 
been sufficiently ample to give them good working form, but 
has perhaps been sufficient to show their general relationship to 
an atmospheric hypothesis of glaciation. 
The hypothesis here offered is confessedly connected in my 
own mind with these ulterior and more fundamental hypotheses, 
but it does not seem to me that it is necessarily so connected. 
To be sure, if it is assumed, following a prevalent custom of the 
past, that the original atmosphere was a vast gaseous envelope 
embracing essentially all the carbonic acid that is now locked 
up in limestone and other carbonates, and all that is represented 
by coal and other carbonaceous matter, and that the atmospheric 
history has been essentially a progressive depletion of this origi- 
nal supply, I do not see how the proposed hypothesis can be 
entertained, at least for the earlier glaciations. But if it be 
tA Group of Hypotheses Bearing on Climatic Changes, Jour. GEOL., Vol. V, 
No. 7, 1897. The Ulterior Basis of Time Divisions and the Classification of Geologic 
History, zd2d., Vol. VI, No. 5, 1898. A Systematic Source of Evolution of Provincial 
Faunas, 7bzd., No. 6, 1898. The Influence of Great Epochs of Limestone Formation 
upon the Constitution of the Atmosphere, z/¢¢, Lord Kelvin’s Address on the Age 
of the Earth as an Abode Fitted for Life, Science, N. S., Vol. [X, No. 235, pp. 889— 
901, June 30, 1899, and Vol. X, No. 236, pp. 11-18, July 7, 1899. 
