PERMIAX ELEMENTS IX THE DUXKARD FLORA 541 



The above list might be largely increased from the species found in the Mononga- 

 hela formation. The species quoted are, however, among the more widespread 

 Coal Measures tj^pes. Over one-half of their number are common plants in the 

 Allegheny or Conemaugh formations. 



The Dunkard plants indicate the presence in the Appalachian trough of a tran- 

 sition from the Coal Measures to the typical Permian floras. Such a transition in 

 the plant life is only natural in a region where the terrestrial conditions continued 

 essentially the same, and where there was uninterrupted deposition with but slight 

 and very gradually introduced chaiiges in the sedimentation. The circumstances 

 were most favorable for the persistence of species, and it is therefore not suprising 

 that we find modified representatives of such common Coal Measures types as 

 those recorded in the report under Neuropteris hirsuta, N. flexuosa, and Aanularia 

 sphenophylloides continuing in the greatest abundance to the top of the formation. 

 The conditions being continuity of sedimentation, with but slight and gradual phys- 

 ical changes, accompanied by a transitional flora, it is proper to assume that any 

 changes in the flora would be chiefly the results either of climatic modification or 

 of migration from some region experiencing more pronounced physical changes. 

 The determination of the boundary between the Coal Measures and the Dyas is 

 therefore to be governed by the appearance in the region of characteristic Eoth- 

 liegende species rather than by the presence of persistent Coal Measures types. 



As the stages are now generally' characterized paleobotanically in western Europe, 

 the presence of representatives of the genus Callipteris, the simple-fronded Tseniop- 

 teris, Callipteridium of the types gigas or regina, and the genus Walchia, in a flora 

 largely composed of types common also to the Coal Measures, is regarded as suffi- 

 cient evidence of Rothliegende age, although CaUipteris coiiferia and rare examples 

 of Walchia may occur in the preceding stage. In the Appalachian region CaUip- 

 teris conferta has not yet been found below the Lower Washington limestone, about 

 175 feet above the base of the Dunkard, where a small variety is present along 

 with a form of C lyratifolia, while the larger, typical form and C. curretiensis, to- 

 gether with Callipteridium gigas and Odontopteris obtusiloba, are not yet known below 

 the Dunkard coal. 



The evidence of Eothliegende age for the beds below the Washington limestone 

 consists chiefly in the presence oi Equisetites rugosus and the less important, though 

 at least to some extent characteristic, Goniopteris newberryana, Pecopteris germari, 

 Caidopteris gigantea, Sphenophyllum fontaineanum, and Sigillaria approximata in the 

 roof of the Waynesburg coal, at the base of the formation. To this is to be added 

 the occurrence at this level of the special types of Mesozoic or Permian aspect, 

 especially the Equisetites striatus, the two species of Saportsea, the Baiera, the lobed 

 Teeniopteris, as well as the Pecopteris pachypteroides, P. dentata var., and P. \_Callip- 

 teridium ?^ unitum. To these might also be added the species of later facies or affin- 

 ities listed in the earlier part of this summary. However, the weight of the latter 

 evidence is possibly counterbalanced by the remarkable rarity of all but the last 

 mentioned species, none of which has yet been found elsewhere than in a portion 

 of a single one of the numerous drifts about Cassville, West Virginia, although 

 careful search for them has been made in the same and higher horizons at Cass- 

 ville and other localities. 



On account of the small number of species which may be considered as in a 

 measure characteristic of the Rothliegende, the absence from the latter of Callip- 

 teris, the old world Dyassic Odontopteris and Callipteridium, and the extreme 



