of the Alleghany Mountain Range, 531 



Feet. 



The carboniferous series as before - 1000 



Old red sandstone, and shales, passing into grauwacke! 



shales, slates, and argillaceous sandstones, with Pro- J- 5000 to 7000 

 ducta, &c. - - - - J 



Highly inclined grauwacke slates, and other argillaceous beds, \ „ n0ft 



some of them slightly calcareous, with encrinital casts J 

 Grauwacke sandstones and grits - 2500 



Transition limestone, often siliceous, one bed being oolitic - 5000 

 Ferruginous sandstones and conglomerates - - 2000 



Limestones and grauwacke rocks, in vast thickness, beneath. 



From these statements will be seen how enormous is the 

 developement of the beds immediately succeeding to the se- 

 condary roGks of this region* 



By a series of instrumental observations, made in the 

 coal region we are proceeding to describe, it appears that 

 the coal measures vary in elevation above the sea (at the 

 distance of 180 miles from it) from 1560 ft. to 2100 ft., in 

 the counties of Lycoming, Bradford, and Tioga. Here the 

 coal is disposed in two principal basins, those of Lycoming 

 and Tioga. They are based upon a series of hard conglo- 

 merates and grits, which originally, formed one vast con- 

 tinuous platform, now cut through and furrowed down by 

 innumerable watercourses, which form? narrow ravines and 

 gorges many hundred feet in depth.. The coal area, which 

 once was a coextensive deposit, stretching widely across the 

 country, is thus cut into a series of insulated patches, which, 

 from the undulations of their planes, now present the appear- 

 ance of, and in fact are, really separate mineral basins, capping 

 the summits of some of the highest table-lands. 



Having extensively studied the structure of this part of the 

 bituminous coal district, I am satisfied that it is to the undu- 

 lating character of the coal strata, in the aggregate, that the 

 circumstance of the presence or absence of the mineral: por- 

 tions must be mainly ascribed, the intervals between these 

 small coal fields being several miles. Hence the concave 

 portion of the undulations, being less exposed to the destroy- 

 ing agency of alluvial causes, in slow but constant and gigantic 

 operation, remains undisturbed in its basin, while the convex 

 parts of the rolling strata have, in every instance within my 

 knowledge, been partially or entirely swept away ; it being 

 obvious that the soft argillaceous beds of the coal measures 

 would be the first and the most effectually acted upon by at- 

 mospheric and superficial causes. It is this physical character 

 or structure which has preserved the coal basin of Blossburg 

 on the Tioga, and which has left bare an extensive area to 



p p il 



