HYPOTHESES BEARING ON CLIMATIC CHANGES 679 
constant atmosphere, but their occasional failures to run in 
consonance are herein assigned as possible causes of exceptional 
climatic episodes, for it is almost axiomatic to say that climatic 
changes would attend changes in the constitution of the atmos- 
phere. I assume that atmospheric poverty, especially in the 
critical item of carbon dioxide, is correlated with low tempera- 
ture, as urged by Tyndall and others. 
It is impossible here to attempt to apply the doctrine in 
detail to geological history. But it may be noted in passing 
that the Pleistocene glaciation followed at a notable interval the 
formation of the great plateaus and epeirogenic uplifts of late 
Tertiary times. The glaciation of India, Australia and South 
Africa occurred about the the time of the crustal revolutions 
that marked the close of the Paleozoic era. The uncertainty 
of the homotaxis of the strata involved makes a precise cor- 
relation at present impossible. The glaciation perhaps came too 
early to fitthe hypothesis.t. Here, at least, is an excellent chance 
to put it to trial. Allother hypotheses of glaciation have fared 
badly when brought to the supremely severe test of the ancient 
oriental low-latitude glaciation, and if this hypothesis shall fol- 
low them to the junk shop of broken down theories it will find 
an already beaten path. The glaciation of northern Norway 
as determined by Reusch and Strahan succeeds the pre-Cam- 
brian stage of elevation, but in what precise relations is not 
known. 
The great extensions of warm climate to the high north 
appear to be associated with baseleveling periods in a general 
way ; but whether ina specific connection of sufficiently declared 
nature to indicate the relation of cause and effect remains to be 
determined. 
Another source of atmospheric depletion needs recognition. 
Dr. S. W. Johnston is responsible for the opinion that the entire 
carbon dioxide of the atmosphere would be removed by the pres- 
ent annual growth of vegetation if there were no return through 
decomposition and animal life provided it were continued uni- 
‘It may fall under the organic factor of the hypothesis mentioned later. 
