DIFFERENT PROVINCES OF NORTH AMERICA IN LATE PALEOZOIC TIME 75 



Virginia. The area covered was originally much larger, as outliers are 

 found in Pennsylvania, West Virginia, and Maryland; all evidence of the 

 original extent to the east has been removed by erosion. 



David White 1 is quoted by Stevenson to the following effect from a 

 revision of the original work by I. C. White and Fontaine on the flora of 

 the Dunkard: 



The fauna of the Dunkard is placed in 5 categories: 



a. Those characteristic of the Rothliegende or higher 12 species. 



b. Those clearly allied to Permian types 12 species, 



(but the number might be extended). 



c. Those whose habit and facies suggest a late date, all new and unknown elsewhere, suggest 



later date than the Coal Measures 14 species. 



d. Those of Mesozoic aspect, important as nearest relatives are Mesozoic 9 species. 



e. Coal Measure types, widespread forms 29 species. 



David White considers the Dunkard flora as transitional between the 

 Permian and the Coal Measures, the beginning of the former being deter- 

 mined by the first appearance of the Rothliegende forms. He considers 

 the beds below the lower Washington limestone as transitional beds; above 

 this the flora contains an increasing number of Rothliegende forms. The 

 flora of the upper Dunkard is to be compared with that from Stockheim and 

 Cusel in Germany and Drives in France. 



The persistence of a large number of Coal Measure forms and the well- 

 known and repeated occurrence of more rapid evolution in floral elements 

 than in the faunal elements in geological time makes this certainly as good 

 an argument for Permo-Carboniferous age as for Permian and in no wise 

 militates against drawing the Permo-Carboniferous line at a lower level. 

 (See also I. C. White's note of the discovery of Callipteris in the upper 

 half of the Conemaugh, as reported by David White, cited on page 66.) 



Stevenson continues: 2 



"None of the characteristic coniferous genera Ullmania, Tylodendron, Walchia, 

 occurs in Dunkard beds, though all are in Prince Edward Island and Walchia is 

 reported from Texas [and New Mexico Case] ; and similarly many genera of ferns 

 characterizing the Rothliegende of Europe seem to be wholly unrepresented. ' 



"The general physical conditions during Allegheny and Conemaugh were 

 practically the same; for, while the basin was contracting, there was no material 

 variation in character of the movements; but with the beginning of Monongahela 

 the area of greatest subsidence was shifted a hundred miles and the new condition 

 remained unaltered throughout the Monongahela and Washington, which in 

 this respect are one as the Allegheny and Conemaugh are one. A notable 

 change occurred in the Washington, and Mr. White has shown that the strongly 

 marked lower Rothliegende flora makes its appearance near the bottom of the 

 Greene formation." 



In these remarks concerning the similarity of the Allegheny and Cone- 

 maugh, Stevenson is not in agreement with other writers, who see a decided 

 difference between the two series. 



1 White, David, Permian Elements in the Dunkard Flora, Bull. Geol. Soc. Amer., Abstract, 



vol. xiv, pp. 538-542, 1903- 

 1 Loc. cit., p. 173. 



