Physical Theory of Secular Changes of Climate. 487 
There is another class of facts, almost entirely overlooked, 
which prove even more conclusively the warm character of 
interglacial periods. These facts will, however, be more appro- 
priately discussed when we come to consider the question ot 
warm polar climates. 
It would be impossible within the limits of the present. 
paper to give even the briefest outline of the recent discover- 
les in regard to interglacial periods. But though this were 
edit it would be wholly unnecessary, as the facts which 
ave already been adduced by Mr. Wallace himself are per- 
fectly sufficient for our present purpose. 
If now it be true, ‘as it undoubtedly is, that the Hessle 
bowlder-clay of England belongs to the same age as the pper 
Till of Scotland, and that the last warm interglacial period, 
when the Cyrena fluminalis and Unio littoralis, the bippo- 
last and penultimate ice-sheets was not so great as to warrant 
the supposition of any considerable difference in the amount 
of eccentricity at the two periods when these ice-sheets were 
respectively developed. In short, if the last great ice-sheet 
ean be explained without the supposition of a high state of 
eccentricity, then there does not appear to be any real necessity 
for any theory of eccentricity in accounting for the Glacial 
h 
dvocate ; 
_ and equable condition of 
