64 H. D. MACGINITIE 



similar mean temperature for the polar seas. Brooks (1951, p. 1005) 

 independently arrived at the same figure for polar oceanic tempera- 

 tures in the Middle Tertiary. 



When warm surface water extends far to the north, atmospheric 

 and oceanic circulation must profoundly modify polar climates. 

 Any permanent ice caps would be impossible under such conditions, 

 although winter snows north of the Arctic Circle would be probable. 

 "Extended and bitter arctic cold" around the poles would not be 

 possible with the indicated ocean temperatures of the Upper Cre- 

 taceous and Lower Tertiary. The polar forests of those times were 

 deciduous, and it is a reasonable assumption that the deciduous 

 habit, at least in part, arose in response to photoperiodicity, as an 

 adaptation to the long period of winter darkness in polar regions, 

 rather than as an adaptation to thermoperiodicity. 



If we turn to the Lower Tertiary, there is again abundant evidence 

 for the existence of a temperate deciduous forest occupying a zone 

 around the Pole. Several well-known localities are well within the 

 Arctic Circle. According to the best evidence available, these i\rcto- 

 Tertiary Geo-floras, as they have been called (Chaney, 1947, pp. 

 144-146), range in age from Paleocene to Middle Eocene. Some nota- 

 ble localities (Seward, 1933, pp. 408, 478-479) are in eastern Green- 

 land (70°-75° N. Lat.), Spitzbergen (78° N.), Elsmereland and 

 Grinnell Land (to 83° N.), the McKenzie River Delta (64° N.), and 

 the New Siberian Islands (75° N.). Farther south, to latitude 55° 

 N. in the central part of the continents, are many more fossil locali- 

 ties of this northern, summer-green forest. Among the characteristic 

 trees are the dawn redwood, ginkgo, sycamore, alder, oak, chestnut, 

 poplar, hazelnut, and many close relatives of trees now growing in 

 the deciduous forests of the Appalachians and eastern China. It 

 was, in no sense, a <:6>/(i-temperate flora. The species would find a 

 congenial habitat at present in the mountains of western North 

 Carolina at moderate elevations. 



In the early Tertiary as well as in the Cretaceous there was a 

 zonal distribution of forests around the Pole that points clearly to 

 the fact that the Pole was in the same place as it is today (Chaney, 

 1940). There was a gradual transition from the tropical floras of the 

 Gulf states to the warm-temperate floras of Yellowstone Park and 

 southern Canada and thence to the temperate deciduous floras of 

 the far north. We can now amend the quotation given at the begin- 



