36 Dr. J. Croll on Aretie 
time that it lived there. Before doing so, it may be as well 
to glance at what evidently were the main characteristics of 
the interglacial periods. 
Main Characteristics of Interglacial Climate——They are as 
follows :— 
1. Interglacial conditions neither did nor could exist simul- 
taneously on both hemispheres. ‘They existed only on one 
hemisphere at a time, viz. on the hemisphere which had its 
winter solstice in perihelion. 
2. During interglacial periods the climate was more equable 
than it is at present; that is to say, the difference between 
the summer and winter temperatures was much less than it is 
now. The summers may not have been warmer or even so 
warm as they are at present, but the temperature of the 
winters was much above what it is at the present day. 
3. During interglacial periods the quantity of equatorial 
heat conveyed by ocean-currents into temperate and polar 
regions was far in excess of what it is at present. On this 
account a greater uniformity of climate then prevailed : that 
is to say, the difference of climatic conditions between the 
subtropical and the temperate and polar regions was less 
marked than at present—the temperature not differing so 
much with latitude as it now does. 
4. Mildness, or a comparative absence of high winds, cha- 
racterized interglacial climate. ‘This partial exemption from 
high winds resulted from the fact that the difference of tem- 
perature between the equator and the poles, the primary cause 
of the winds, was much less than at the present day. 
5. Another character of interglacial climate was a higher 
mean temperature than now prevails. This, amongst other 
causes, resulted from the great amount of heat then transferred 
by ocean-currents from the glacial to the interglacial hemi- 
sphere. 
6. During interglacial periods the climate was not only 
more equable, mild, and uniform than now, but it was also 
more moist. This was doubtless owing mainly to the fact of 
the presence then in temperate and polar regions of so large 
an amount of warm intertropical water. In short, it was the 
presence of so much warm water from intertropical regions 
which mainly gave to the climate of the interglacial periods 
its peculiar character. 
All these characteristics of interglacial climate have been 
fully established by the facts of geology, but they are also, as 
we have secn, deducible @ priori from physical principles. They 
follow as necessary consequences from those pliysical agencies 
which brought about the glacial epoch. 
