17b* I). WHITE — RELATIVE AGES OF KANAWHA-ALLEGHENY SERIES 



grated en masse, so the flora as a whole appears in the Kanawha region 

 in nearly its exact Pennsylvanian composition and facies ; (/) under 

 the above conditions it is unreasonable to suppose that a migration, as- 

 suming such a one to have occurred, of less than 300, probably less than 

 150, miles* would have required so long a period as that represented 

 in the sedimentation of the lower half of the Kanawha formation. 



The far greater migration of the interglacial flora in pursuit of the re- 

 treating ice must, as timed by the comparatively thin sediments formed 

 under the most favorable conditions during the Pleistocene period, have 

 required but a relatively short interval. Furthermore, if it be assumed 

 that during earlier Kanawha time the marsh or peat bog which repre- 

 sented the depository of each of the Allegheny coals stretched practically 

 continuously from the Allegheny Valley region to the Kanawha region, 

 as is implied by the correlations and usage of the West Virginia geol- 

 ogists, we must believe that several floras would have been met by the 

 traveler in passing from south to north across the great marsh or bog, a 

 condition which would indicate a difference of climate in Carboniferous 

 time far greater than that to be found under similar circumstances within 

 the same latitude at the present day ; or, if we suppose the coals to have 

 been formed by notation of the carbonaceous matter, a theory in many 

 cases more satis factoiy, it becomes probable that an intermingling of the 

 species from different portions of the basin would have occurred in the 

 quiet waters of plant deposition. 



Since it is generally admitted that the Pottsville formation, which is 

 said to be represented by but 160 feetf of sediments in the Broad Top 

 coalfield of southern Pennsylvania, attains a thickness of over 2,000 

 feet in the southern Virginia region, it is not improper to assume, on the 

 other hand, that in the great expansion of the formation the upper beds 

 ma}'' have lost their distinctive massive conglomeratic character and 

 merged horizontally into shales, sandstones, coals, etcetera. 



That such a change occurred is indicated by the observed distribution 

 of the Pottsville floras, the apparent overlap of the lowest Kanawha floras 

 on the type paleontologic section of the Pottsville, and the notable dif- 

 ference between the typical Upper Pottsville flora of the type section and 

 the lowest flora of the typical Allegheny series. This difference is so 

 great as to suggest that the group of upper conglomerates forming a 

 plexus with the " Buck Mountain conglomerate " in the Southern An- 

 thracite field, or perhaps the Homewood sandstone in the Allegheny val- 



* The actual discrepancy between the geological correlations and the evidence of the fossil plants 

 occurs within the geographic interval between the Potomac basin and the Kanawha river, a dis- 

 tance of less than 150 miles. 



t Bull. U. S. Geol. Survey, no. 65, p. 185. 



