AN ATTEMPT TO FRAME A WORKING HYPOTHESIS 
OF THER CAUSE OF GLACIAL PERIODS ON AN 
MUMOSERMERIC - BASIS * 
THERE are hypotheses and working hypotheses. The sugges- 
tion that the last glacial period was caused by the passage of the 
solar system through a cold region of space may be styled a 
hypothesis, but scarcely a working hypothesis in the geological 
sense, for it does not form the groundwork or incentive of 
geological inquiry. An astronomer might be moved to hunt 
for the cold spot, but it has no inspiration for the geologist. 
General suggestions of a possible cause do not reach the dignity 
of working hypotheses until they are given concrete form, are 
y/ fitted in detail to the specific phenomena, and are made the 
' agents of calling into play effective lines of research. The con- 
struction of a concrete working hypothesis suited to stimulate 
and guide investigation in a wholesome manner, and to take its 
place in competition with other hypotheses of like working 
potentialities, thereby inducing a more searching scrutiny of 
the phenomena and a more varied application of interpretations, 
represents the higher limit of present reasonable aspiration. It 
is much too ambitious to hope for a demonstrative solution of 
the origin of the earth's glacial periods by first intention in the 
present state of knowledge. 
The hypothesis here offered is not worked out into satisfac- 
tory detail at all points, but it is hoped that it is sufficiently 
matured to justify a preliminary statement. In forming it, 
which has been the work of several years, I have found, or 
seemed to find, the phenomena of past glaciation intimately 
associated with a long chain of other phenomena to which at 
* A brief statement of the salient features of this hypothesis was given in a paper 
entitled A Group of Hypotheses Bearing on Climatic Changes, Jour. GEOL., Vol. 
V, pp. 653-683, Oct.-Nov. 1897. For earlier history see footnotes on pp. 654 and 681 
of that paper. 
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