1883-1884.] 26l 



There is no stratlgraphical break, but there is a break all round 

 the Arctic Circle in the continuity of the floras, for unfossili- 

 ferous sedimentary beds 1,000 feet thick often intervene between 

 the highest of the ^so-called Cretaceous and the lowest of the 

 so-called Miocene plant beds, and these unfossiliferous beds 

 represent, according to Heer, the Eocene. Now no reason has 

 ever been advanced why the Eocenes should alone be unfossili- 

 ferous in high latitudes. It is universally admitted that con- 

 tinuous land existed in the north between Europe and America 

 from early Eocene times, as proved by the palseontological 

 records of both continents, as well as by many other facts. 



The discovery of a flora at the base of our Eocene formation, 

 implying a climate as temperate as that we now enjoy, accounts 

 for the unfossiliferous zone in the deposits of the far north, 

 for under such conditions, no forests of leafy trees would be able 

 to flourish in Greenland and Spitzbergen, and to this age it may 

 safely be referred ; but the increase of heat that took place 

 towards the middle Eocene, when the temperature in the 

 latitude of London became almost tropical, would certainly 

 drive vegetation very far northward ; indeed, it is only common 

 sense to suppose that the hottest period of the Tertiary would 

 be the one most likely to produce a luxuriant vegetation round 

 the Arctic Circle. I assume, from all the data I have collected, 

 that the mean temperature of the South of England, (lat. 50°,) 

 was some 70° Fahr., and if the temperature decreased in going 

 north at approximately the same ratio as it does to day, 10° Fahr. 

 for every 10° latitude, we should have a mean temperature of 5°F. 

 in Greenland under latitude 70°, which is exactly the Miocene 

 temperature (9o°C.) assigned to it by Heer. The decrease from 

 Greenland to Grinnell-land is in about the same ratio, and Heer 

 admitted that the fossil Tertiary plants show a corresponding 

 decrease as far north as Spitzbergen, though he disputed, against 

 the evidence I think, that it was maintained to Grinnel-land. 

 With our Middle Eocene temperature sub-tropical in lat. 50°, 

 we need feel no surprise at the presence of such floras in high 

 latitudes. England and Greenland of the past were relatively 



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