CHAF. IX.] 
GEOLOGICAL CLIMATES. 
201 
addition to the altitude of our islands could have brought about 
the extreme amount of glaciation which they certainly under- 
went, and when, further, w r e know that a phase of very high 
excentricity did occur at a period which is generally admitted 
to agree well with physical evidence of the time elapsed since 
the cold passed away, there seems no sufficient reason why such 
an agency should be ignored. 
No doubt a prejudice has been excited against it in the minds 
of many geologists, by its being thought to lead necessarily to 
frequently recurring glacial epochs throughout all geological 
time. But I have here endeavoured to show that this is not a 
necessary consequence of the theory, because a concurrence of 
favourable geographical conditions is essential to the initiation 
of a glaciation, which when once initiated has a tendency to 
maintain itself throughout the varying phases of precession 
occurring during a period of high excentricity. When, however, 
geographical conditions favour warm Arctic climates — as it has 
been shown they have done throughout the larger portion 
of geological time — then changes of excentricity, to however 
great an extent, have no tendency to bring about a state of 
glaciation, because warm oceanic currents have a preponderating 
influence, and without very large areas of high northern land 
to act as condensers, no perpetual snow is possible, and hence 
the initial process of glaciation does not occur. 
The theory as now set forth should commend itself to geolo- 
gists, since it shows the direct dependence of climate on physical 
processes which are guided and modified by those changes in 
the earth’s surface which geology alone can trace out. It is in 
perfect accord with the most recent teachings of the science as 
to the gradual and progressive development of the earth’s crust 
from the rudimentary formations of the Azoic age, and it lends 
support to the view that no important departure from the great 
lines of elevation and depression originally marked out on the 
earth’s surface have ever taken place. 
It also shows us how important an agent in the production of 
a habitable globe with comparatively small extremes of climates 
over its whole area, is the great disproportion between the 
extent of the land and the water surfaces. For if these 
