RELATION TO FLORA OF POTTS^ILLE SERIES. 307 



most beds of the Westphalian, while the Pittsburg coal of the bituminous 

 basius^ aud the G coal of the Northern Anthracite field are clearly referable 

 to the Stephanian (Ottiveiler Schichten). 



There is a strongly marked contrast between the known flora of the 

 lowest coals of Missouri, Illinois, Indiana, Ohio, and western Pennsylvania 

 and that of the Pottsville series, or Millstone grit, which lies in most cases 

 close beneath them, there being in fact relatively few species in common. 

 Tlie latter flora agrees in its later phases with the flora of the Millstone 

 grit of Europe. 



The Lower Coal Measures of Great Britain and the zone of Vicoigne 

 in the Franco-Belgian Basin, with their intermingling of Millstone grit or 

 Culm species with the earliest of the Coal Measures types, appear, so far 

 as we know at present, to be unrepresented by any interval in the Lower 

 Productive Coal Measures in the bituminous regions mentioned above. It 

 is not improbable, however, that this interval is concentrated in some cases 

 in the deposition of the highly variable upper benches of the Pottsville series 

 in the Northern States, rather than that it is represented by a time break or 

 that there is homotaxis without contemporaneity in the floras. For in the 

 greatly expanded sections of the Lower Coal Measures in the Kanawha 

 region in West Virginia, which is in the same Appalachian trough aud was 

 throughout Mesocarboniferous time united with the northern areas by con- 

 tinuous shore lines, the characteristic forms of the lowest coals of the Lower 

 Productive Coal Measures of the States north of the Ohio and Potomac 

 rivers are not met until we arrive at a point several hundred feet above tlie 

 Pottsville series as hitherto limited. The floras of the Kanawha series, 

 extensive collections from which are now in my hands for examination, 

 will be found to show a lower zone of mingled types, corresponding very 

 closely to the Lower Coal Measures of Great Britain or the lower zone of 

 the Franco-Belgian Basin. 



' The flora of the Freeport coals is so nearly unknown that its relations to the floras of any- 

 other stage outside of the anthracite series is still quite uncertain. 



