358 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



south over Europe and America, and although somewhat older 

 than the last, is distinctly related to that in Argentina. 



On passing up in the geologic time scale we find that durmg late 

 Mesozoic and early Ceno zoic time the present dominant types of vegeta- 

 tion were firmly established. With what probability of success may 

 these floras be interrogated as to the climatic conditions under which 

 they existed ? We find from a study of the present flora that certain 

 types of vegetation, as well as certain plant associations, have definite 

 climatic requirements. Thus, Artocarpus, or the bread fruit trees, 

 are now confuied to within 20° of the Tropics, showmg that they 

 require the moist heat of the torrid regions. If, now, we fiiid that 

 Artocarpus once throve in Greenland, 70° or more north, during Cre- 

 taceous time, we feel justified in assuming that its climatic require- 

 ments were not very different from those of its living representatives. 

 And when we fuid that it was then in association, as it is to-day, 

 with cycads, tree ferns, cinnamons, palms, and other distinctly 

 tropical forms we are confirmed in the opinion that at that time 

 Greenland must have enjoyed a tropical or at least a subtropical 

 climate. 



Another example is afforded by the Fort Union formation. In 

 the rocks of this horizon, which now occur on the wind-swept, almost 

 treeless plams of the Dakotas, Wyoming, and Montana and thence 

 northward to the valley of the Mackenzie, are found remains of 

 Sequoia, Taxodium, Thuya, UJmus, Populus, Vitis, Platanus, Sapin- 

 dus, Viburnum, Corylus, Juglans, Hicoria, etc. From this array we 

 feel justified in assuming a cool to mild temperate climate for this 

 early Eocene flora, and further, from the presence of numerous, often 

 thick, beds of lignite, that there was a much higher precipitation than 

 at present. 



A layer of fan-palm leaves a foot m thickness in a formation hi 

 northern Washmgton mdicates climatic requirements m which the 

 minimum temperature did not fall much if any below 42° F. The 

 presence of numerous West Indian types in the Miocene lake beds of 

 Florissant, Colo., would alone point to almost tropical conditions, but 

 as these are associated with others of more northern affinities, it 

 seems safe to predicate at least a warm temperate or possibly sub- 

 tropical climate. 



