358 F. H. KNOWLTON C'RITEKIA I'OK DETERMINATION OF CLIMATE 



a considerable assemblage of species. This distribution shows conclu- 

 sively that there was not only free communication between the Eastern 

 and Western Hemispheres, but also between the Northern and Southern 

 Plemispheres, and, as none of the Jurassic plants is known to possess any 

 peculiar mechanism for dispersal, it is apparently clear that there must 

 have been a continuous or practically continuous land connection through- 

 out this vast area. It is also evident, that this wide distribution could 

 only have been possible under very uniform climatic conditions. Such a 

 distribution would be utterly impossible under the present zonally dis- 

 posed climates. 



Without attempting to present a complete analysis of this flora (for 

 which see my paper, "Evolution of geologic climate"), the conclusion is 

 reached that the presence of luxuriant ferns, many of them tree-ferns, 

 equisetums of large size, cycads, and conifers, the descendants of which 

 are now found in warm lands, all point to a moist, warm, probably sub- 

 tropical climate. 



The Upper Cretaceous Atane flora of Greenland may be briefly con- 

 sidered. This flora ranges from Greenland along the Atlantic Coastal 

 Plain and Gulf region to Texas with but little change, and the Dakota 

 flora spread with practically no change from Minnesota, ISTebraska, and 

 Kansas to Argentina. The inference to be drawn from these facts is that 

 during Upper Cretaceous time the temperature conditions were very uni- 

 form over the greater part of the earth's surface, extending from at least 

 72° north in Greenland to at least 60° south in Argentina, with the 

 probability that it was practically world-wide, A study of these floras 

 reveals very little evidence of deciduous habits, which implies an unin- 

 terrupted growing season and an abundant, or at least adequate, supply 

 of moisture, well distributed throughout the year. The coal deposits of 

 Upper Cretaceous time also imply widespread and long-continued swamp 

 or marsh conditions. 



In the Atane flora there are such genera or Artocarpus (breadfruit- 

 tree), Cinnamomum, Laurus, Pseudocycas, Aralia, Panax, Cyathea, 

 Gleichenia, Widdringtonites, etcetera, which are largely tropical or sub- 

 tropical in distribution. Associated with them are such genera as Acer, 

 x\splenium. Cassia, Cissites, Diospyros, Hedera, Ilex, Magnolia, Myrsine, 

 Paliurus, Pinus, Pteris, Quercus, Sapindus, Selaginella, etcetera, which 

 while having more or less representation in temperate regions many have 

 representatives in warm temperature and even subtropical regions. Prom 

 this it seems safe to conclude that the climate of Greenland during Atane 

 time could not have been cooler than warm temperate, and when we con- 

 sider the presence of breadfruit-trees, figs, cinnamon trees, tree-ferns, 

 etcetera, it might well have been subtropical. 



