Marsh Collection, Peabody Museum. 421 



That the animals and plants lived and died in the vicinity 

 where their fossil remains occur ; and (2) that by comparison 

 with their nearest living allies we may deduce some informa- 

 tion respecting their habits. For example, we know that such 

 plants as Palms, Oycads, and Tree-Ferns require a given mean 

 temperature for their existence. Frost quickly destroys them 

 and they rapidly disappear where much freezing takes place. 

 Their northernmost limit is found, therefore, at or near the 

 isothermal line separating a warm temperate from a subtropical 

 temperature. Thus, while a few of the hardier forms may be 

 distributed along the borders, the vast majority of the species 

 inhabit the more central tropical and subtropical parts of the 

 earth, where they form a conspicuous and characteristic feature 

 of the flora. 



If, therefore, the remains of such forms as Palms, Cycads, 

 or Tree-Ferns occur as fossils in a given locality, we may 

 conclude without fear of error that the temperature of such 

 place could not have been below that which at present limits 

 their distribution, yet it may at the same time have been tropi- 

 cal or subtropical. Some information regarding the latter 

 condition may be had from the relative abundance of remains 

 of such species. If very abundant and in considerable variety, 

 a subtropical or tropical temperature rather than that border- 

 ing on a warm temperature would be indicated. In the same 

 way, we may assume the presence of remains of certain species 

 of extinct animals to be indicative of, and equally conclusive 

 proof of, temperatures in which their nearest allies live at the 

 present day. 



With this understanding of the nature of the evidence upon 

 which we must rely, I pass next to a brief review of the former 

 distribution of the plants in the Northern Hemisphere, and, 

 shall begin with a consideration of the fossil florse of the Arctic 

 regions. Certain deposits in Greenland, near Disco Island, 70° 

 33' N. Lat. — the Kome beds — have yielded a rich flora, which 

 according to Heer, its describer, is strictly comparable with 

 that of the Neocomian or Lower Cretaceous of Europe and 

 America. It includes Ferns, Cycads, Conifers, and a single 

 species of Angiosperm — a Poplar. Of the Ferns, the genus 

 Gleichenia, now almost exclusively tropical in its distribution, 

 is represented by fifteen species. There are also four genera 

 of Cycads, with numerous species, whose nearest living repre- 

 sentatives now inhabit the tropical and subtropical regions. 

 Pines, Redwoods, and other Conifers, some closely related species 

 to which are now found living in China and California, go to 

 make up the list of the Gym nos perms. The Angiosperms, as 

 far as we now know, are represented by the single genus and 



