PERMIAN. 493 



separation. These, as -will be seen, appear only in part along Dunkard Creek, where Dr. White's 

 studies led him afterward to group the whole succession into one formation, the Dunkard. 

 They are best shown farther north, in central Greene County, where they justify a return to 

 the original grouping and to the recognition of the Washington and Greene formations as of 

 equal rank with the Monongahela and others below. 



In the Washington and Greene formations, which compose the Dunkard , 

 group, Stevenson distinguishes sixteen and eighteen members respectively, alter- 

 nations of coal, limestone, and sandstone. 



The comprehensive study of the Dunkard flora by Fontaine and I. C. White ^** 

 was revised by David White.*^'' Stevenson^*' reviews the evidence as follows: 



The results of this revision were published in 1903. The collections, made at the typical 

 as well as at other localities and horizons, led 'Mr. [David] White to place the forms in five cate- 

 gories — (a) those characteristic of the Rothliegende or higher formations of the Old World; 

 (&) those closely allied to Permian types; (c) those whose habit and facies suggest a late date; 

 (d) those of Mesozoic aspect; (e) Coal Measures type. 



In the first category Mr. White places three species of Callipteris, one each of Goniopteris, 

 Pecopteris, Alethopteris, Odontopteris, Caulopteris, Equisetites, and Sigillaria, with two species 

 of Sphenophyllum; in all, 12 species. In the second are also 12, but the author states that the 

 number might be extended according to the personal equation of the observer or to the amount 

 of material available for comparison, while, at best, evidence of this class is of subordinate 

 value, some of the forms placed here belonging with equal propriety also in succeeding cate- 

 gories. 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 

 suggest types characteristic of Mesozoic. Here are species of Equisetites, Saportsea, Jean- 

 paulia, and Tseniopteris, as well as other genera. On the other hand are forms belonging to 

 the fifth category, a considerable element of Coal Measure species, whose presence is invincibly 

 against reference of the beds to a level above the basal Permian. The number of species com- 

 mon to the Dunkard and lower formations, only 22 at the time when Profs. Fontaine and I. C. 

 White published Iheir work, is now laiown to be much greater, as the Monongahela flora has 

 been studied in part. Mr. White enumerates 29 common forms wliich are of ordinary occur- 

 rence 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 would be expected in a 

 region where conditions remained practically the same. The boundary between Coal Measures 

 and Dyas is to be determined by the appearance of characteristic Rothliegende species rather 

 than by the presence of persistent Coal Measure types. In western Europe the presence of 

 CaUipteris, simple fronded Tseniopteris, Callipteridium of the gigas or regina type, and the genus 

 Walchia in a flora consisting largely of forms common to the Coal Measures is regarded as suffi- 

 cient evidence of Rothliegende age, though Callipteris conferta and even Walchia 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 Callipteridium 

 gigas and others, is unknown below the Dunkard coal bed. The evidence of Rothliegende age 

 for beds below the Lower Washington limestone consists in the presence of Equisetites rugosus 

 and several less important forms and of some others which have Mesozoic or Permian aspect; 

 but these latter are extremely rare, having been found 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 tran- 

 sitional flora and not distinctly Rothliegende, but above that limestone the flora becomes increas- 

 ingly characteristic. As in that limestone is the first appearance of Callipteris conferta, he 

 thinks the lower limit may be drawn safely at that horizon. The flora of the upper Dunkard 



