EVIDENCE OF FLORAS AS TO ISOSTATIC MOVEMENT 177 



ley, may represent a much greater time interval than is inferred from 

 their proportionate thickness. 



EVIDENCE OF THE FLORAS AS TO THE ISOSTATIC MOVEMENT IN THE 

 SOUTHERN VIRGINIAN REGION 



The paleontologic observations made by me in the field are too incom- 

 plete to warrant more than an outline of the development of the indi- 

 cated dilations. An examination of the fossils from the Allegheny series, 

 as the latter has been stratigraphically traced in the Potomac basin in 

 northern West Virginia, shows but little, if any, change in the normal 

 position of the floras as far south as Thomas, in Tucker county, where 

 the series is said * to be 273 feet in thickness. 



Any great diagonalling, therefore, whether of floras or lithologic 

 boundaries, must have occurred south of this region, or within 125 

 miles of the Kanawha and along the shore of the basin. A hasty ex- 

 amination of the available material leads me to believe that a slight 

 change in the lithology of the uppermost beds of the Potts ville occurred 

 in the region of Pickens, while on the Holly river, within 50 miles of 

 the Kanawha, the absence of the typical Allegheny flora for some dis- 

 tance above the lithologic Pottsville boundary is noticeable. The field 

 and plant data at hand indicate that the dilation and transformation of 

 the beds immediately below the base of the Allegheny series progress 

 rapidly from Sutton to the mouth of Twenty Mile creek. This most im- 

 portant change becomes more and more marked in proceeding along the 

 margin of the coalfield from Holly river to the mouth of Gauley river, 

 though the lithologically new, intermediate, sub- Allegheny series (Ka- 

 nawha in part) seems to expand somewhat farther to the southwest. 



The development and expansion of the terranes forming the lower 

 half of the Kanawha formation, as distinguished lithologically from the 

 Pottsville, occur in the same direction and in the same region as the 

 great expansion of the Pottsville formation. The latter formation, 

 which is but little more than 400 feet in thickness at Piedmont, on the 

 Potomac river, or 733 feetf on the Blackwater, in Tucker county, and 

 which appears to be but about 500 feet in Webster county, rapidly 

 thickens along the basin of the Gauley river to over 1,600 feet where it 

 meets the Kanawha river. The evidence of the fossil plants shows that 

 the isostatic movement in the southern Virginian region which rendered 

 possible the deposition of about 2,400 feet of distinctly Pottsville sedi- 

 ments in that portion of the Appalachian trough continued under con- 



*Op. cit.,p. 127. 



f Bull. U. S. Geol. Survey, no. 65, p. 187, 



XXV— Bull, Geoj,. Soc. Am., Vo&, 11, 1899 



