18 The Twenty-third General Meeting. 
to find that man co-existed in our woods and valleys—on Salisbury 
Plain, and on the banks of the Avon—with animals which are now 
to be found only in remote regions or which are altogether extinct. 
It is sufficiently surprising to reflect that on this very spot where 
we are now assembled there once ranged large herds of those strange 
and gigantic animals; but another most interesting consideration 
is, that when we come to consider them more closely, we shall see 
that they constitute in reality two distinct groups. The hippopo- 
tamus, for instance, and probably the hyena, extended into Great 
Britain, the porcupine into Belgium, the African elephant into Spain 
and Sicily, facts all indicating a climate warmer than the present. 
On the other hand the mammoth and the long-haired rhinoceros, 
the reindeer and the marmot, the Arctic hare and fox, the ibex, 
chamois, and the musk-sheep, point decidedly to Arctic conditions. 
The musk-sheep, indeed, has the most northern range of any known 
mammal. Passing over for the present those mammalia which seem 
to indicate a tropical climate, let us consider what may be called the 
Arctic group, and I may observe in passing that the existence of a 
very cold climate during the latest geological period had been in- 
ferred from other considerations, even when our knowledge of the 
mammalian fauna was much less considerable and consequently less 
suggestive. Various theories have been suggested to account for 
the fact that at a period, geologically speaking so recent, the climate 
of Europe should have been so different from what it is at present, 
and the best authorities seem now to consider that the true explanation 
is to be found in astronomical causes. If the plane of the equator 
coincided exactly with that of the ecliptic every day would be suc- 
ceeded by a night of equal length. In consequence, however, of the 
obliquity of the ecliptic, this only happens twice in the year, namely, 
on the 20th of March, and 23rd of September, which days divide 
the year into two halves, the day being longer than the night in the 
spring and summer, and shorter, on the other hand, in autumn and 
winter. Under existing circumstances then, we have in the northern 
hemisphere seven days more of summer than of winter, while in the 
southern hemisphere they have, on the other hand, seven days more 
of winter than of summer. ‘This, however, has not been, nor will it 
