Vol, 58.1] CONDITIONS OF THE PLEISTOCENE EPOCH. 43 
ed on purely geological and paleobotanical grounds, amount 
70,000 and even 100,000 years. Thus my estimate, founded 
on astronomical and phy sical grounds, seems’ to give a fairly 
average value between the highest and lowest estimates of the . 
geologists, 
To conclude with a general observation on Mr. Harmer’s paper, 
I cannot but think that he underrates the thermal effect of insolation, 
and overrates that of the winds. In order to appreciate the exact 
value of every cause, it is necessary to make quantitative calculations 
and measurements. If we do this, we find that the effect of inso- 
lation during summer far exceeds that of the winds during the 
same season. The temperature of the summer only is 
essential for the phenomenon of glaciation. 
Discussion. 
Mr. Harwer thanked the Author for his paper, as being likely to 
arouse an interest in the study and discussion of paleeometeorology. 
He still adhered, however, to the opinion which he had expressed, that 
the influence of the winds must have been a very important factor in 
the determination of climatal zones during the Pleistocene Epoch, as 
it undoubtedly is at the present day. If the distribution of pressure 
and the consequent direction of the prevalent winds which then 
obtained could be ascertained by the joint efforts of geologists and 
meteorologists, it would throw much light on the history of the 
Glacial Pernt: 
He could not admit that there was the same difference between the 
winter-temperature of North America and Western Europe as that 
which now exists. At present the winter-isotherm of 32° Fahr. ex- 
tends 30° of latitude farther northward in the latter than its southern- 
most limit in theformer. It is true that the ice-sheets are supposed 
to have reached farther to the south in America, but the principal 
centre of ice-accumulation in Europe was situated many hundred miles 
farther north than that of the Laurentian region. The gathering- 
ground of the ice was, moreover, more extensive in the latter case. 
Had the mountain-region of Scandinavia extended over France and 
the plains of Northern Germany to the Alps and the Pyrenees, the 
European ice-sheet would no doubt have assumed much larger pro- 
portions. No important ice-centres are recorded in North America 
farther south than the latitude of Switzerland, to which the in- 
fluence of Glacial cold certainly extended, and there seems no valid 
reason for supposing that the winter-climate of New England was 
much more severe at the climax of the Ice-Age than that of the last- 
named country. If this was so, it seemed in favour of the hypothesis 
that the maximum glaciation of the Eastern and Western Hemi- 
spheres may not have been contemporaneous. He had shown that 
during the winter of 1898-99 excessive cold (reaching —60° Fahr.) 
lasted for many weeks in North America, coincidently with an 
abnormally mild season in Europe, a maximum temperature of 
70° Fahr. being recorded at Liége, 134° above the American 
