FLORAL CHANGES IX POTTSVILLE TIME. 307 



stratigra})hic examination of the New River section, made in order to 

 ascertain the general relations of the major divisions of the series there, 

 together with the contained coals, to the Pottsville series in other por- 

 tions of the eastern Carboniferous basins, as well as to establish a palcon- 

 tologic section for com})arison of local floras in the central portion of the 

 Appalachian region. Although the work on the section is not yet com- 

 pleted, it is thought^tlie facts ascertained are of sufficient interest to 

 justify a preliminary i)ublication. 



So far as the discussion concerns other regions, the evidence considered 

 will be mostly paleontologic and therefore chronologic. 



Rapid Differentiation of and Change in Floras during Pottsville 



Time. 



It should be remarked at the outset that wherever plants have been 

 gathered from several liorizons in thick sections of the Pottsville in dif- 

 ferent portions of tlie Api)alacliian belt, a careful scrutiny of the speci- 

 mens shows a distinctly notable difference between the floras gathered at 

 intervals of several hundred feet in the same section. Indeed, the period of 

 change in conditions of environment attending the transition from T^ower 

 Carboniferous marine to true Coal Measures formation was marked by 

 an extraordinarily rapid development and modification of vegetaljle 

 species. \\'ithin a relatively short i)eriod the meager flora of the De- 

 vonian and Pocono is multiplied to the inexhaustibly fecund and highly 

 diversified flora of the Carboniferous, a development scarcely possible 

 except in this division of organic life, which is the most sensitive to 

 climatic change or environment, excepting perhaps the higher verte- 

 brates. In the lower j^art of the Pottsville series many species show a 

 relation to the floras of the Vespertine or Calciferous Sandstone series ; 

 in the middle portion many of the forms are uhifpie, while in thickly 

 developed sections it is only near the top of the series that we see occa- 

 sional Coal Measures forms creeping in. 



These modifications and differentiations of forms have l)cen found to 

 be fairly consistent and generally constant in their relative {)osition in the 

 various sections thus far examined. This is true even of those very dis- 

 tant, but l>ecause the modification of a i)lant from one stage to another, 

 though representing a definite i)hase or form, is often not sufficient to 

 constitute a distinct species, and because these stratigrapbic modilica- 

 tions of species have received little or no attention in our American 

 literature on Paleozoic j)lants, I shall fre<iuently l)e ol)liged to refer to 

 them as forms, designating them by the name of somtj locality or well 



