VESPEKTINK GROUP. PP. 5 



group only 200 feet thick on the Potomac River, near the 

 villages of Westernport, in Hampshire Co. W. Va. From 

 this point of miniumm development it thickens to the 

 northeast, southeast, and west, but much more rapidly in 

 the two directions first named. Towards the northeast, in 

 Huntingdon Co., Pennsylvania, according to Mr. Ash- 

 burner, it is 2133 feet thick, with a coal bearing member 

 near its center, 303 feet thick, which contains 19 small seams 

 of coal.* 



Traced to the southeast, in Montgomery Co. Va. we 

 lind it nearly 2700 feet thick, and containing, as previously 

 stated, two important coal beds. 



While the group, as a rule, becomes much thinner as we 

 follow it to the west, yet traced in this direction from West- 

 ernport, the locality of its least development, it thickens. 

 Hence in the eastern part of Monongalia Co. W. Va. on 

 Cheat River, as recently determined by us, it is over 500 

 feet thick, the base not being seen. 



The physical character also changes, as shown in the 

 western exposures, for we find on Cheat River the follow- 

 ing strata in descending order : 



1. Lower Carboniferous (Umbral) Limestone. 



2. Flaggy Sandstones. 90 feet. 



3. Massive White Sandstone. 100 feet. 



[*Tliat is, 2133 feet up to the base of the red beds beneath the Mountain 

 Limestone. Mr. Ashburner very properly excluded these red beds from the 

 Vespertine, and considered them the lower member of the Umbral. I cannot 

 agree "with Professors Fontaine and White in thinking that "it seems best in 

 W. Virginia " or any where else "to place them with the underlying Vesper- 

 tines into which they " certainly do not, at least along an outcro23 of 150 miles 

 in Pennsylvania, " pass by insensible gradations." 



The Mountain Limestone is an interpolated deposit in the red shales, since 

 it thins away to nothing in eastern Pennsylvania; in Middle Pennsylvania 

 not only lies 141 feet above the well marked lower limit of the red shales, but 

 it is itself nothing but a group of frequently alternating red shales, red shaly 

 limestones, red silicious limestones, variegated red and grey limestones, red 

 and grey mottled calcareous shales, (fee, through a vertical space of 45 feet. 

 There seems to me no more reason for making the Mountain Limestone of 

 XI a horizon line separating two great formation, than for using the Ji^cm/er- 

 OMS Xi'mesiowe of the Lower Productive Coal Measures, or the Great Lime- 

 stone of the Upper Productive Coal Measures for that purpose. At all events, 

 any such line of demarkation would be absurd for the nomenclature of our 

 Anthracite Coal Region. — J. P. L.] 



