282 GEOLOGY. 



strongly in contrast witli the floras of the same region at the present 

 time. Curiously enough the Miocene plants of Alaska, Kamschatka, 

 and Japan indicate a climate cooler than that of the higher latitudes. 

 It seems probable that this apparent discrepancy is the result of imper- 

 fect correlation, the fossils indicating these inharmonious conditions 

 not being contemporaneous. If this is the explanation of the apparent 

 anomaly, the subtropical floras of the high latitudes are probably 

 earlier than the other floras with which they have been compared. 

 In any case, the existence of warm temperate conditions in such high 

 latitudes in such recent times is remarkable, especially when it is 

 remembered that extensive ice sheets were soon (geologically speak- 

 ing) to affect not only these regions, but regions much farther south. 

 It is worthy of emphasis that throughout all lands where the Mio- 

 cene system is known, terrestrial aggradation seems to have been one 

 of the leading features of the period. Terrestrial aggradation implies 

 still greater terrestrial degradation, and relatively great relief. The 

 necessary relief seems to have been the result of the crustal move- 

 ments which brought the Eocene period to a close. 



The Life of the Miocene. 

 The Land Plants. 



The flora of the Miocene in the mid-latitudes differed from that 

 of the Oligocene chiefly in the gradual disappearance of the character- 

 istic subtropical types, and in an increased proportion of deciduous 

 forms, especially of those that are now present in the same regions. 

 This is particularly true of North America, where the flora came to 

 resemble that which to-day lives in somewhat lower latitudes, and is 

 indeed its successor. The flora of Europe bore a similar " American " 

 aspect, but this it has not retained in an equal degree. This is attributed 

 by Zeiller to the barrier to southern migration interposed by the Med- 

 iterranean during the ice invasions of Pleistocene times, a barrier which 

 prevented the plants from escaping southward, and led to the destruc- 

 tion of many species which subsequent migration from other regions did 

 not restore. In Europe there were also, in the early part of the 

 period, not a few species now found in India and Australia, giving, 

 as in the previous period, an " Australian " sub-aspect to the flora. 

 A very important feature in North America was an increase in the 



