I04 The American Geologist. Angast, i8si* 
more extended than at any other period. The author would 
define the beginning of the Ice age to be that period when 
the oceans ceased to receive heat from the bottom, and began 
to accumulate water at its maxinuun density; the culmination 
of that age to be that period when solar heat began to perma- 
nently remove glacial conditions and to establish its control 
of surface temperatures. It is reasonably certain that glacial 
conditions were first removed from the torrid zone. It is 
probable that maximum giaciation along the belt of maximum 
precipitation in the northern hemisphere about lat. 50° oc- 
curred subsequent to the culmination of the Ice age, and that 
maximum giaciation of polar regions occurred at a still later 
period. Thus glacial conditions may have been cumulative 
upon successive portions of the globe. The Ice age has long 
since terminated in tropical regions, more recently in temperate 
latitudes and yet remains within the polar circles; from which 
the present indications, as interpreted by the author, are that 
it is destined to disappear and be replaced by polar snow caps, 
which, like those of Mars, form and melt away with the sea- 
sons. 
In the present condition of science the student is not offered 
a logical explanation of climatic evolution; but instead, is 
presented with a mass of facts, which are interpreted along 
various lines and seem to warrant some writers in the conclu- 
sion that in the evolution of climates, there have "been changes 
from cold to warmth and back again to cold." This whilst 
true in a restricted sense is not so broad as to include the re- 
currence of general glaciations, or successive glacial epochs. 
With a vast array of facts at command — with a remarkably 
intimate knowledge of past life-conditions, there has never- 
theless been recorded a complete failure to arrive at satisfactory 
conclusions as to the cause of the secular variations in climate 
which have marked geological history. Such failure results 
from the introduction of radical errors, from the omission of 
fundamental principles, or from a misconception of the char- 
acter of the problem. When any one, or any combination of 
these misleading factors, is permitted to enter into so compli- 
cated a problem, the human mind, although yearning for truth, 
often strays far from it, and resorts to suppositions and hypo- 
theses which cannot be established. The stronger and more 
