157 



LITHOLOGIC CHAEACTEKS AND SECTIONS. As just noted above, the 

 Martinsburg shale consists in general of black shale forming the lower 

 division and light-colored sandy shales the upper, but its lowest beds are 

 of thin-bedded limestone and calcareous shale, while the uppermost beds 

 are gray sandstone. The formation thus includes a variety of rock types, 

 but shale is the predominating rock, so that the lithologic designation 

 " shale " for the formation as a whole is appropriate. Depending more 

 particularly on fossil evidence, four distinct divisions can be recognized 

 in this shale, although all may not be present in the same section. These 

 divisions with their approximate thicknesses are expressed in the fol- 

 lowing general section : 



General Section of the Martinsburg Shale in Southern Pennsylvania 

 and Maryland 



Juniata Formation of Earliest Silurian or Highest Ordovician Age. 



Martinsburg shale. 



Upper Maysville division. Feet 

 Unfossiliferous sandstone (Oswego sandstone). (Probably 

 represented under cover west of North Mountain, in Mary- 

 land) 150 



Lower Maysville division. 



Fossiliferous gray sandstone with Orthorhynchula linneyi bed 

 at top. (Probably present west of North Mountain under 



cover) 300 



Eden division. 



Yellow shale and calcareous sandstone interbedded, with upper 



Eden fossils 500 



Soft greenish to yellow shaly sandstones and shale with Eden 



fossils not uncommon at several horizons 500 



Trenton and ? Utica division. 



Dark-gray unfossiliferous shale breaking up into " shoe peg " 



fragments and often weathering into soft whitish clay. . . 500 



Black carbonaceous fissile unfossiliferous shale 500 



Calcareous dark shale and thin limestone weathering gray 



containing graptolites (Corynoides fauna) .20-100 



Granocrystalline fossiliferous limestone and shale holding the 



Sinuites fauna 2-10 



Chambersburg limestone 



Total 2500 



