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 w^hen, further, we 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 Avarm 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 

 ea>rth'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 



