Geology and Mineralogy. ' 461 



southern Appalachians before the Black shale invasion, for in the 

 region of Covington, Va., this may be seen resting at times on 

 the Oriskany or the Becraft limestone, which is very well devel- 

 oped here. About Cumberland, Md., the maximum thickness for 

 the Oriskany is about 300 feet. In sections only a few miles 

 apart the thickness will vary from this down to 50 feet, and 

 these thinner sections always carry a Lower Oriskany fauna, 

 indicating a land interval here subsequent to the Upper Oriskany 

 and before the Marcellus. The writer knows of no typical Onon- 

 daga (Corniferous) faunas south of northeastern Pennsylvania, 

 and the faunules listed in this Bulletin, as, for instance, 1382 B3 

 and 1383 A2 and 3, are decidedly more Marcellus than Onondaga. 

 Owing to the irregular pre-Marcellus erosion producing an uneven 

 topography, it follows that the invading base of the Black shale 

 will be different in different places. It is the writer's working 

 hypothesis that owing to the Onondaga erosion interval and the 

 low-lying fold which delimited the western boundary of the 

 Cumberland Basin, the base in different localities may be any- 

 where between basal Marcellus and the higher Devonic. The 

 Helderbergian and Oriskanian deposits are in full development 

 in Mainland, but thin out rapidly southward, and none attain 

 very far south of the Tennessee- Virginia boundary line. The 

 Manlius, Coeymans, and New Scotland are typically present as 

 far south as Hancock county, Tenn. The Becraft is in full force 

 about Covington, Va., but is gone before Big Stone Gap is 

 reached. The Lower Oriskany is present in the Hicksville, Va., 

 faunule 1379 Al, but no Upper Oriskany. In other words, the 

 waters of the Cumberland Basin extend from Hancock county, 

 Tenn., north into Pennsylvania, throughout Manlius, Coeymans, 

 and New Scotland time. With the Becraft there begins an 

 emergence at the south, slowly dissipating the sea to the north, 

 so that Oriskany sediments do not appear much south of Coving- 

 ton, Va. In Maryland the sea is continuous from the early 

 Siluric to the end of Oriskany time, when emergence also sets in 

 here and affects the Appalachian trough as far north as north- 

 eastern Pennsylvania. 



Along the eastern side of the Cincinnati axis the invading 

 Black Shale is never older than the Genesee. Here, again, the 

 base is variable, but apparently is always within the time of the 

 Genesee. This variability is due not only to the erosion uncon- 

 formities pointed out by Dr. Kindle, but also to the transgression 

 of the Genesee sea upon the Cincinnati axis. 



Several species of the Buchiola speciosa (— _#. retrostriata) 

 fauna have their first appearance in the Marcellus and are apt to 

 recur throughout the higher Devonic whenever the Black shale 

 conditions prevail. Most of its species have a long range, as may 

 be seen from the table on pp. 51, 52, of this Bulletin. Here 25 

 species are positively identified. If Anoplotheca acutipllcata 

 occurs in this fauna in Virginia (can it be a Vitulina ?) no partic- 

 ular time value can be assigned to it against the 24 other asso- 



