W. J. McGee—Theory of Glacial Climate. 119 
annual precipitation, or of the combined values of the glaciation- 
factors, be excessive, the computed rate of ice-accumulation is 
too rapid; while if they be defective, the importance and effi- 
ciency of eccentricity as an element in glacial climate has been 
underestimated. 
The foregoing results sustain the opinion of Wallace and 
others as already stated, and show that (presumably) the 
weightiest objection of the recent reviewers is invalid. 
_The third objection of the first reviewer is based on a subor- 
dinate side-question springing indirectly from the Crollian the- 
ory, which may or may not in any way affect the fundamental 
principles of the theory; for the question as to what physical 
effect a given mass of ice will exert on the earth’s center of 
gravity and on the position of the ocean is wholly independent 
of the question as to the reason of Quaternary ice-accumulation ; 
and the validity of the eccentricity theory, per se, is accordingly 
in no way affected by the verity of the phenomena adduced. 
_ Again, the tripartite sequence of Quaternary deposits described 
in the text-book (glacial—aqueous—glacial) does not appear to 
€ so thoroughly understood and so clearly drawn, and the 
consensus of opinion concerning it so uniform, as to allay the 
suspicion that the aqueous beds may be analogous to those 
everywhere deposited during and immediately after the with- — 
rawal of the second ice-sheet. 
This objection, therefore, is also invalid. 
In his first objection the second reviewer overlooks the fact 
(upon which the writer has already had occasion to insist)* that 
the hypothetical deflection of the Gulf Stream, in the manner 
contemplated by Croll, is an effect of glaciation, and, if a cause 
cas 
at all, only a secondary one. Hence if the glaciation-factors 
alone are capable of inaugurating a glacial period, the assistance 
of this element is not essential ; and if they are not alone capa- 
le of producing such an effect, the whole theory fails. 
This objection, too is accordingly incompetent. 
With no desire to underestimate the actual difficulties of the | 
eccentricity theory, or to detract one iota from the laudable 
caution displayed in such general criticism as that of the first 
reviewer, a word may be added with reference to the deprecia- 
tory tone of the class of critics represented by the third reviewer. 
ntricate and far-reaching’ as the theory is, encroaching as it 
oes upon different branches of science, involving as 1t must 
elements seldom codrdinated by individual specialists, 1t requires 
for its thorough comprehension a range of preliminary study 
*8 “ Croll’s ‘Climate and Time’” (review), Popular Science Monthly, xvi, 1880, 819, 
