Vol. 58.] METEOROLOGY OF THE PLEISTOCENE EPOCH. Oo” 
4. On the Merzorotoeicat Conprrions of the Preistocenr Epocu. 
By Dr. Nits Exuorm, Meteorologiska Central-Anstalten, Stock- 
holm. (Communicated by Prof. W. W. Warts, M.A., F.G.S. 
Read November 20th, 1901.) 
Iy his interesting paper entitled ‘ The Influence of the Winds upon 
Climate during the Pleistocene Epoch,’ Mr. F. W. Harmer’ has 
endeavoured to describe the meteorological conditions of that 
epoch by means of the theories and facts of modern meteorological 
science. The subject is no doubt one of great interest, but also 
of great difficulty. We still know too little concerning the 
nature, origin, and development of the great atmospheric eddies, 
the cyclones and anticyclones, to be able to reconstruct their 
average positions and tracks on the globe during a past geological 
epoch. Furthermore, it is very difficult to estimate the influence 
of those eddies on climate. As my opinion on this matter differs 
in some important respects from that expressed in Mr. Harmer’s 
paper, I crave permission to discuss the question briefly. It may 
be conveniently divided under the following heads :— 
(1) What are the meteorological conditions necessary and suffi- 
cient to produce a permanent ice-sheet, or glaciation such as that of 
the Great Ice-Age? 
(2) What will be the influence of such a glaciation on the 
meteorological conditions, especially on the cyclones and anticyclones, 
over the ice-covered land and its neighbourhood ? 
In order to answer these questions we must consider the present 
climatic conditions of the earth, and draw our inferences there-— 
from. 
(1) We know that a land must lie above the snow-line in order 
that it may be glaciated. At first sight, we might be inclined to 
assume that this snow-line coincides approximately with the mean 
annual isotherm of 32° Fahr. But this holds good only in the 
vicinity of the Equator, where the yearly variation of the tem- 
perature of the air is insignificant. The farther we recede from 
the Equator, and the nearer we approach the Poles, the more, as a 
general rule, does the mean annual temperature of the snow-line 
sink below 32° Fahr. This temperature, however, will not vary 
with latitude only, for the quantity, quality, and annual period 
of precipitation [rainfall], and the summer temperature have a 
very marked influence. ‘Thus the centre of cold near Verkhoyansk 
in Siberia, with a mean annual temperature of about 0° Fahr., is 
‘not glaciated, whereas the southern point of Greenland, with an 
annual mean of about 32° Fahr., is covered with a permanent 
ice-cap. Now Eastern Siberia is covered during the whole winter 
by a great anticyclone, the sky is nearly always clear, little or 
no snow falls, and that which does fall is very quickly thawed 
* Quart. Journ. Geol. Soc. vol. lvii (1901) pp. 405-76. 
