CHAP. IX.] 
GEOLOGICAL CLIMATES. 
199 
land was at all times simple in outline ; and its enlargement 
took place with almost the regularity of an exogenous plant .” 1 
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 warm 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 Manual of Geology , 2nd Ed. p. 525. 
