DIFFICULTIES IlST THE WAY OF COREELATIOiS^. 291 



Since the report on these basins was written, comprehensive collections 

 have been made from the lowest coals (including- the Brook-sdlle and 

 Clarion) of the Bernice semi-anthracite basin, the bituminous fields of 

 northwestern Pennsylvania, and the lowest coals above the Potts-salle 

 series in the anthracite regions. But our knowledge of the floras of the 

 different stages above these or the Morris coal of Illinois, and below the 

 Upper Barren Measures (XVI) in the bituminous fields north of the Ohio 

 and Potomac rivers is, with the exception of several small floras in Illinois, 

 practically still limited to the rich collections from the Darlington coal at 

 Cannelton, Pennsylvania; small collections from three or four points in the 

 "Kittanning" in Ohio, and a small number of species from near the Pitts- 

 burg coal at Wheeling, West Virginia, and a few points in Ohio. But from 

 all the bituminous fields of Pennsylvania no systematic collecting of fossil 

 plants has, so far as I am aware, lieen done from any horizon between the 

 Clarion coal in the lower part of the Lower Productive Coal Measures and 

 the Waynesburg coal, except at Cannelton, near the Upper Kittanning. 

 Not only are we ignorant of the floras of the .vai-ious coals in the upper 

 part of the Lower Productive Coal Measures (XIII), or Alleghany series, 

 in that State, but also of the plants of the entire Lower Barren Measures 

 (XIV) and of the Upper Productive Measures, or Monongahela series (XV). 

 With these facts in mind, not only will it be easy to understand the great 

 difficulty in correlating the various stages in the bituminous fields with 

 either definiteness or confidence by means of the fossil plants, but it will 

 also be clear why, in studying the range or correlative affinities of the 

 species in these fields, the smaller or isolated floras are drawn as l)y mag- 

 nets toward the stages of Cannelton or Morris. It is paradoxical that these 

 two stages at Mazon Creek and Cannelton should have been paleobotani- 

 cally exploited nearly to exhaustion, while east of Illinois the plant fossils 

 of the succeeding measures have remained essentially untouched. So long 

 as paleontologists and museum curators remain content with filling their 

 collections from the two famous localities, Cannelton and Mazon Creek, 

 without an effort to ascertain the floral characters of any other stages, 

 we shall continue without knowledge of the paleobotanic characteriza- 

 tions necessary for the definite or satisfactory recognition in the northern 

 bituminous fields of any stage between the Kittanning and Waynesburg 

 coals. 



