HYPOTHESIS OF CAUSE OF GLACIAL PERIODS Wfd 
immediate antecedents and the nature of contemporaneous con- 
ditions in other parts of the world are not yet satisfactorily 
determined. No embarrassment attends a merely general appli- 
cation of the atmospheric hypothesis set forth in this paper, and 
perhaps it would be wise in the present state of knowledge to be 
content with such general application. But the main purpose 
of the paper—to develop a working hypothesis, helpful in the 
promotion of investigation— would be measurably defeated 
thereby, for a general theory merely supposed to be applicable 
in some indefinite way, not even specifically thought out, much 
less shaped to promote definite inquiry, falls short of working 
qualities. Were the Paleozoic glaciation a high-latitude phe- 
nomenon which could be referred to the same category as the 
Pleistocene glaciation, we might well leave specific discussion 
until further data were afforded, for few additional doubts as to 
the verity of the hypothesis and probably few new lines of 
inquiry would be raised. But the Paleozoic glaciation presents 
characters so extraordinary as to render it the supreme problem 
of glaciation. In it every hypothesis finds its severest test. No 
hypothesis that. does not, in some remote way at least, approach 
an elucidation of this supreme case can: have serious claims to 
acceptance as a working theory. It is, therefore, imperative to 
frankly and fully recognize this crucial problem and deal with 
its difficulties as well as existing data permit. <A really satisfac- 
tory discussion is quite impossible in the present nature of the 
case. The attendant atmospheric and geographic conditions 
must be postulated, consciously or unconsciously, but the data 
for such postulates are imperfect and their interpretation is at 
best not more than probable. It is hoped, however, that fairly 
good reasons can be assigned for everything assumed in this 
paper. 
The essential facts that make the Paleozoic glaciation a 
peculiarly strenuous problem are these : 
1. It occurred in an early stage of the earth’s history. No 
appeal can, therefore, be made to an advanced state of secular 
cooling leading on the ‘‘final winter’’ nor to any senile condition 
