292 FLORA OF LOWER COAL MEASURES OF MISSOURL 



COMPARATIVE POSITION OF THE COALS. 



Notwithstandino- the difficulties which attend any attempt to ascertain 

 the contemporaneity of terranes in the upper half of the Mesocarboniferous 

 in the United States, the study of the elements in the floras in hand and 

 their distribution in the lower two-thirds of the Lower Productive Coal 

 Measures, which are better known paleobotanically, shows that the Lower 

 Coal Measures of Missouri, as represented by the coals of Henry County, 

 were laid dowii soon after the Morris coaP in Illinois, though probably earlier 

 than the Upper Kittanning of western Pennsylvania, or very likely about 

 the time of the formation of the D coal in the Northern Anthracite field.^ 

 Thus the chronology of the plants shows that the process of the deposition • 

 of the Mesocarboniferous terranes was well advanced, so that in the bitu- 

 minous fields of Ohio, Pennsylvania, and Illinois not only the Pottsville 

 series (XII), ranging from 60 to 1,200 feet or more in thickness north of the 

 Potomac River, but also the lower portion of the Lower Productive Coal 

 Measm-es, or "Alleghany series" (XIII), extending as far upward at least 

 as the Clarion coal, had been laid down on the Lower Carboniferous (Eocar- 

 boniferous) group b}^ the time the lower coals of Henry County were sedi- 

 mented in fringing ponds or marshes along the coast of eroded Eocarbon- 

 iferous rocks in Missouri. 



It will be remembered that in some places the lower of the two coals 

 (the interval between them being reported as 40 to 60 feet) rests directly on 

 the uneven Eocarboniferous surface, while at other points a variable arena- 

 ceous formation intervenes. The latter, which is very irregular, sometimes 

 conglomeratic, and nowhere of great thickness, appears to represent a wash 

 derived from the decomposed underlying rock, whose hollows it tends to fill, 

 and is generally regarded by the local geologists as belonging to the "Mill- 

 stone grit" (Pottsville). So far as the writer is aware, however, no primary 

 fossils have been procured from it to show its true age, and it would seem 

 that it may represent simply the subaerial surface material of decomposition 

 accmnulated subsequent to the Eocarboniferous uplift and but imperfectly 

 distributed and sorted when the subsidence of the coast brought about the 



' Supposed by many, for stratigrapliic reasons, to be the equivalent of the Clarion coal of the 

 eastern bituminous fielfl, and therefore commonly designated by the same letter (B). 



-The letters in use to designate the coals in the anthracite fields are not to be construed as indi- 

 cating their equivalency with the coals similarly designated in the bituminous regions. 



