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172 J. J. STEVENSON CAEBONIFEROUS OP APPALACHIAN BASIN 



evidence of this class is of subordinate value, some of the forms placed 

 here belonging with equal propriety also in succeeding categories. He 

 places in the third category 14 forms, all of them new and unknown 

 elsewhere; these in their general facies suggest a later date than Coal 

 Measures. He places 9 forms in the fourth category and regards their 

 presence as an interesting and important argument for Permian age, for 

 they are types whose nearest relatives are Mesozoic or whose facies 

 strongly suggests types characteristic of Mesozoic. Here are species of 

 Equisetites, Saportcea, Jeanpaulia, and Tceniopteris, as well as of other 

 genera. On the other hand are forms belonging to the fifth category, 

 a considerable element of Coal Measure species, whose presence is in- 

 vincibly against reference of the beds to a level above the basal Permian. 

 The number of species common to the Dunkard and lower formations, 

 only 22 at the time when Professors Fontaine and I. C. White published 

 their work, is now known to be much greater, as the Monongahela flora 

 has been studied in part. Mr White enumerates 39 common forms which 

 are of ordinary occurrence in the Coal Measures, these being only the 

 more widespread forms, more than one-half of them appearing frequently 

 in the Allegheny or Conemaugh. 



Mr White finds in the Dunkard plants a transitional flora, such as 

 should be expected in a region where conditions remained practically 

 the same. The boundary between Coal Measures and T)yas is to be 

 determined by the appearance of characteristic Eothlic^gende species 

 rather than by the presence of persistent Coal Measures types. In west- 

 ern Europe the presence of Callipteris, simple-fronded Tceniopteris, 

 Callipteridium of the gigas or regina t3rpe, and the genus WalcMa in a 

 flora consisting largely of forms common to the Coal Measures is re- 

 garded as sufficient evidence of Eothliegende age, though Callipteris 

 conferta and even Wakliia may appear lower down. In the Appalachian 

 region a small form of Callipteris conferta appears at the horizon of the 

 Lower Washington limestone, while the typical larger form, with Callip- 

 teridium gigas and others, is unknown below the Dunkard coal bed. The 

 evidence of Eothliegende age for beds below the Lower Washington lime- 

 stone consists in the presence of Equisetites rugosus and several less im- 

 portant forms and of some others which have Mesozoic or Permian 

 aspect; but these latter are extremely rare, having been foimd only in 

 a single coal drift, though careful search has been made for them 

 elsewhere. 



Mr White regards the beds below the Lower Washington limestone as 

 containing a transitional flora and not distinctly Eothliegende, but above 

 that limestone the flora becomes increasingly characteristic. As in that 



