GEOLOGICAL SOCIETY OF PENNSYLVANIA. 



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The oldest or lowest members of the red sand stone 

 group, consisting of various coloured shales, pass insen- 

 sibly into the upper dark shales and limestone shales of 

 the grauwacke group below, whose beds are so much 

 tilted as often to be perpendicular. To the first lime- 

 stone parallel succeeds a vast series of highly inclined 

 undulating and contorted strata ; including granular and 

 crystalline quartzose rocks, calcareous, siliceous, and 

 schistose conglomerates, limestones and marbles, slates 

 and shales ; comprehending within them numerous beds 

 of glance coal, bituminous anthracite, graphitic anthra- 

 cite, radiated and conchoidal anthracite, and several 

 varieties of iron ore. There are also distinctive cha- 

 racters about most of these rocks, familiar to those who 

 have studied them, independent of their order of posi- 

 tion, by which they may be recognized. Their organic 

 remains are peculiar and useful guides. 



The foregoing remarks will be best illustrated by the 

 diagram, pi. 8, fig. 6. It is constructed from exist- 

 ing data, but being necessarily contracted in the longi- 

 tudinal scale, the secondary and transition coals are 

 brought more closely together than a correct scale would 

 exhibit. 



Before quitting this section, let me advert to one re- 

 markable feature in it, which must be more minutely 

 examined hereafter. I refer to the sudden change of 

 inclination in the whole mass of stratified rocks, secon- 

 dary as well as transition, about ten miles in advance of 

 the Alleghany mountain ; by which circumstance they 

 dip in opposite directions, not in a limited space, but 

 through a wide area. So extensive is the result of this 

 fracture, whether proceeding from a central upheaving 



bears in many respects a close resemblance, I find myself differing from an 

 authority deservedly high amongst our continental geologists. Mr M'Clure 

 has seen reason to place the old red sandstone on the east side the area occu- 

 pied by the transition, while I recognize it on the west side. 



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