CHAP. IX,] 



GEOLOGICAL CLIMATES. 



199 



land was at all times simple in outline ; and its enlargement 

 took place with almost the regnlarity of an exogenous plant." ^ 



A similar development undoubtedly took place in the Euro- 

 pean area, which was apparently never so compact and so little 

 interpenetrated by the sea as it is now, while Europe and Asia 

 have only become united into one unbroken mass since late 

 Tertiary times. 



If, however, the greater continents have become more compact 

 and massive from age to age, and have received their chief 

 extensions northward at a comparatively recent period, while 

 the antarctic lands had a corresponding but somewhat earlier 

 development, we have all the conditions requisite to explain 

 the persistence, with slight fluctuations, of Avarm climates far 

 into the north-polar area throughout Palaeozoic, Mesozoic, and 

 Tertiary times. At length, during the latter part of the 

 Tertiary epoch, a considerable elevation took place, closing up 

 several of the water passages to the north, and raising up ex- 

 tensive areas in the Arctic regions to become the receptacle of 

 snow and ice-fields. This elevation is indicated by the abundance 

 of Miocene and the absence of Pliocene deposits in the Arctic 

 zone and the considerable altitude of many Miocene rocks in 

 Europe and North America; and the occurrence at this time of 

 a long-continued period of high excentricity necessarily brought 

 on the glacial epoch in the manner already described in our 

 last chapter. 



We thus see that the last glacial epoch was the climax of a 

 great process of continental development which has been going 

 on throughout long geological ages ; and that it was the direct 

 consequence of the north temperate and polar land having 

 attained a great extension and a considerable altitude just at 

 the time when a phase of very high excentricity was coming on. 

 Throughout earlier Tertiary and Secondary times an equally 

 high excentricity often occurred, but it never produced a glacial 

 epoch, because the north temperate and polar areas had less 

 high land, and were more freely open to the influx of warm 

 oceanic currents. But wherever great plateaux with lofty 

 mountains occurred in the temperate zone a considerable local 

 1 3Tanml of Geology^ 2nd Ed. p. 525. 



