GEOLOGICxiL SOCIETY OF PENNSYLVANIA. 



183 



side) which hold a course apparently parallel with the 

 Alleghany range for an undefined extent; and one great 

 line of depression* at the junction of their inclined planes, 

 occasioned by subsidence from the saddles of those 

 planes. 



It is only by enlarged researches; and by the accumu- 

 Ip^tion of more facts in this intricate region, that the pre- 

 cise limits of the configuration^ which I have indicated, 

 may be fully defined. 



Returning now to the controverted subject of the 

 eastern boundary of the Bituminous Coal Field. The 

 parallel of Sideling mountain, ascribed by the author of 

 the report we have quoted, as the supposed eastern limit 

 of this coal field, is the same as Path mountain in Cen- 

 tre county, being apparently an extension of that ridge; 

 and if the same geological parallel be pursued to the north 

 east, it would include all the anthracite of Nescopec, 

 Wilkesbarre and the vicinity of the North branch of the 

 Susquehanna. On the contrary, it has been shown that 

 the secondary formations do not cross the older rocks 

 nor pass the Alleghany ridge ; which must 'therefore be 

 held as the frontier line between the bituminous coal 

 field and the deposits comprehended under the general 

 denomination of the grauwacke groupe. In the five 

 detailed sections of different parts of this ridge, con- 

 structed by myself, and in that recently sketched by Mr 

 E. Miller, the true structure of this great mountain range 

 and its relative connection with the older rock forma- 

 tions, are completely elucidated, and one uniform ar- 

 rangement is proved to prevail. PI. 8, fig. 6. 



Much confusion, at various parts of the eastern vicin- 

 ity of the Alleghany range, has arisen by conferring 

 that name upon many of the parallel transition ridges 

 in advance of it. By some these longitudinal ridges 

 have, with equal impropriety, been styled spurs of the 

 Alleghany; an appellation which their internal structure 



