247 



derived from the study of their vegetable fossil remaios will have a 

 great degree of positiveness aud reliability. 



Researches iu the vegetable world of the old periods of our earth are 

 now pursued with great activity by some of the greatest and noblest 

 minds of Europe. From Greenland to Italy, from the borders of the 

 Atlantic and of the Mediterranean in France to the eastern limits of 

 Russia, specimens of fossil plants are collected, sent to museums, 

 examined and described by authors of celebrity, and their valuable 

 works constantly discover a greater importance in vegetable paleon- 

 tology. In this country, this branch of science has few adherents ; for 

 the reason, perhaps, that we lack till now good collections and special 

 libraries, and also because it is not of immediate application to the 

 material welfare of the human race. It has, however, kept pace with 

 the prodigious scientific development of the last quarter of the cen- 

 tury. In 1850, the fossil land-j^lants known from the iSTorth American 

 formation were only eighteen species, described by Brongniart in 

 his Vegetales fossiles, from specimens sent to him from the Ooal-Meas- 

 ures by Professor Silliman. At the present time, more than one thou- 

 sand species have been described from the various geological formations 

 of this country. A number of students are, moreover, ardently search- 

 ing for and gathering specimens; and the museums of natural history 

 of the best scientific schools have a section for vegetable paleontology. 



Already the study of the North American fossil plants has supplied, 

 in regard to the distribution of the species at different periods, some 

 important information, which modifies a few of the conclusions derived 

 from European vegetable paleontology. Though the isothermal zones 

 have been evidently of a width proportionate to the age of the geological 

 periods, producing in the Carboniferous times, for example, uniformity 

 of vegetation over the whole northern hemisphere, if not over the whole 

 surface of the earth, it appears that there was already at this i)eriod a 

 continental or local facies marked in the groups of vegetation. The 

 North American character is recognized in the coal flora of this conti- 

 nent by Schimper, in his Vegetable Paleontology, as it has been for a long 

 time exposed by the works and descriptions of American authors, and 

 this facies becomes more and more distinct in the more recent periods. 

 The precedence of vegetable types in the geological flora of this conti- 

 nent is distinctly recognized, and, therefore, the hypothesis of the deri- 

 vation of the North American flora from Miocene European types is 

 necessarily set aside. On this last question, former remarks in this paper 

 prove the unity of the present flora, derived by constant succession of 

 related vegetable forms from the Cretaceous at least. On the question 

 of precedence of vegetable types, it has been remarked that the appear- 

 ance of land-plants is positively recognized in the Silurian of Michigan, 

 while no land-plants have as yet been described from formations lower 

 than the Middle Devonian of Europe; that also we find already in the De- 

 vonian of the United States, trunks of Conifers recognized as prototypes of 

 the Araucaria, which are only found later, in the Subcarboniferous of Eu- 

 rope. Our Carboniferous flora has a number of its forms appearing later 

 in the Permian of Europe. The Triassic flora of Virginia and North 

 Carolina is half Jurassic. A number of Cretaceous genera of the Dakota 

 group are reproduced iu the Miocene of Europe, as they are, too, in some 

 of the North American Tertiary vegetable groups, and also in the flora 

 of this epoch. Therefore, the relation of the European Miocene seems 

 partly referable to the American Cretaceous. And in following the com- 

 parison upward, we find, iu what is considered the Eocene of the Lignitic 

 of the Eocky Mountains, a larger number of forms identical or closely 



