814 FLORAL ZONES OF THE POTTSVILLE FORMATION. 



descriptive, aiul illustrative data, (luestions of equivalence or con- 

 temporaneity will ))e restricted to a few of the most important and 

 best-known floras. Iii the later publication it is my intention to 

 diseuss the character, range, and sequence of the floras .somewhat 

 in detail, and to suggest such correlations of the numerous terranes of 

 the formations, known often under different names in different regions 

 and States, as are indicated by the very voluminous collcH'tions in hand, 

 covering both the vertical range and the greater part of the areal 

 extent of the formation in the Appalachian province. 



CLARK FORMATION. 



In passing from the Southern Anthracite field southward by way of 

 the thinner developments of the Pottsville formation in the Broad Top 

 and Potomac regions, we do not, so far as is at present known, meet with 

 so low a phytiferous horizon as that of Lykens coal No. 5 until we 

 approach the basin of the New Eiver in south-central West Wv- 

 ginia, where within the rapidly deepening sections the Pocahontas and 

 Clark formations appear in the basal portion of the Pottsville forma- 

 tion. Paleontologically, one of the most interesting of the floral zones 

 in this region is that represented by the plants in the roof shales of the 

 Pocahontas coal (360 feet above the Mauch Chunk formation) in the 

 Great Flat Top region of Virginia and West Virginia. In these shales, 

 which comprise the basal portion of the Clark formation, we find a flora 

 containing the greater number of the species found over Lykens coal 

 No. 5 and presenting the precise f acies of the latter, including the invari- 

 ably and almost exclusively abundant Neuro}}terh Pocahontas. The 

 preponderance of identical species, the composition of the flora, and the 

 relations of the latter to the succeeding floras render it certain that 

 the horizon of the flora of Lykens coal No. 5 is, in the great Flat Top 

 region, not far from the Pocahontas coal. The question whether its 

 more precise horizon is above or below the latter coal will be discussed 

 in the monograph, when all the evidence is presented. It may, how- 

 ever, be here stated that it can not be far above the Pocahontas coal, 

 nor is it likely to be over 200 feet below it. The zone of this flora, 

 which has ])een identified through the Tazewell, Pocahontas, Oceana, 

 and Raleigh (quadrangles, might ap})ropriately be designated the Xturop- 

 teris Pocahontas zone, though in the Virginia region, as in the Southern 

 Anthracite field, varieties of this species are found in higher terranes 

 of the Pottsville formation. This zone includes the basal portions of 

 the Welch formation in the Tazewell quadrangle;^ the Clark forma- 

 tion in the Pocahontas^ and Oceana quadrangh^s; and a portion, above 

 the middle, of a unit Avhich Mr. ]\I. R. Campbell in the manuscript folio 

 relating to the Raleigh quadrangle has named the Thurmond formation. 



1 Geologic Atlas of the United States, folio 44. 



2 Op. cit., folio 20. 



