GEOLOGICAL SOCIETY OF PENNSYLVANIA. 



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is found at this place, having a roof of black shale 4 feet 

 thick, upon which is an unstratified bed of argillaceous 

 rock, containing a great variety of shells and other ma- 

 rine remains, with sulphuret of iron and balls of iron 

 stone. The upper part of the stratified shale also con- 

 tains marine impressions, and some of the more delicate 

 remains have been replaced by sulphuret of iron. In 

 breaking these rocks to pieces to facilitate their removal, 

 great numbers of shells were loosened and fell out. Spe* 

 cimens 16 to 24, locality k. 



The only limestone I have found in that part of the 

 coal measures shown in the section, is the silicious bed at 

 / previously described, and a stratum 3 feet thick of a 

 light blue colour, which shows itself in the ravine of 

 Ben's creek, at and also in that of Limestone run, 

 which obtains a name from it. The sandstone is very 

 various in appearance and quality. Where it crops out, 

 the strata are frequently so much broken by seams and 

 fissures, as to be unfit for building purposes. The best 

 quarries are usually found in the water courses ; the same 

 causes which swept away the softer strata not having 

 been sufiicient entirely to carry off or destroy the sand- 

 stone, which remains in large blocks on the surface of 

 the ground. 



