The Cause of the Glacial Epoch. — Reed. 1 1 3 
were periods of temperate, mild, climate, rich in all forms of 
life, and that at least one of the periods was of ver)- long- 
duration, — perhaps as long as from the last retreat of the 
ice until the present. 
The assumption that such periods were caused by 
"fluctuations of the fading earth heat" does not seem hardly 
sufficient to account for such long, widespread climatal 
changes as seem to have existed. 
Nor is the theory entirely satisfactor)' with regard to 
unglaciated areas. The presence of lacustral deposits and 
forest beds between the lava sheets indicates that very often 
a considerable lapse of time occurred between successive 
lava flows. So that, if there was any radiation of heat from 
these lavas in Quaternary time, we should expect it would 
be from different and perhaps widely separated flows. 
Probabl}' at no time was heat escaping simultaneously from 
the entire plain. 
The atmospheric currents, passing eastwards from this 
lava plain, must needs have crossed the high ranges of the 
Rocky mountains. The consequent cooling and expansion 
of the air would cause copious precipitation upon the west- 
ern slopes of the mountains; while the winds descending the 
eastern slopes would be cool and dr}-. The influence of the 
neighboring continental ice sheet would also aid in further 
reducing the temperature of the Missouri valley. But, 
granting that there were tributaries from the west pouring 
streams of warm water into the Missouri, we must not for- 
get the thousands of streams from the great ice bod}- on the 
north and east which were pouring in their turbid, icy con- 
tents and effectually lowering the temperature of the river. 
Then after all this we have no explanation of the un- 
glaciated area in northern Alaska. 
In the main, however, the author recognizes and gives 
prominence to some important factors which have been 
hitherto omitted from such hyjiotheses, because thev are 
not striking or conspicuous. 
The day is passing when scientists seek to emplo}- strik- 
ing or extraordinary phenomena in the solutions of their 
problems; rather are they looking to that which appears in- 
significant and commonplace. 
