THE MOUNTAIN. 93 



of its highest knobs, as already remarked, are formed of 

 these rocks, which are all here found dipping in one general 

 direction, exhibiting a vast monoclinal axis of gentle inclina- 

 tions. The northern and western range of these silicious 

 masses give a more broken, undulating, and irregular chain 

 of heights, extending west from Towanda by Blossburg, in 

 Tioga county, the northeastern limit of the bituminous coal, 

 and north of Smithport, in McKean county, and Warren, 

 in Warren county, from which it is slightly deflected, with 

 greatly reduced altitude, somewhat to the south, in the re- 

 gion of Meadville, in Crawford county, and crossing into 

 Ohio through the county of Trumbull. Along the northern 

 side of this basin all the formations, from the olive slate to 

 the coal measures inclusive, have gentle southern dips, and 

 the passage into the large basin is successively over higher 

 and higher strata from the New York line, where the slates, 

 shales, and argillaceous sandstones of the olive (Formation 

 8) slate formation are the predominating rocks. In Craw- 

 ford and Mercer counties, where the lower strata crop out 

 northwest of the coal, the general dip is southeast ; while 

 on the southeastern margin, or in the range of the Alleghany, 

 the prevailing inclination is north of west ; thus inward all 

 round toward the centre of the great trough containing the 

 coal. While this is true with regard to the edge of the 

 large basin, within this boundary there are a number of 

 arches or anticlinal axes, some of which are of great length 

 and considerable elevation, others low, with slight inclina- 

 tions, giving to the entire mass of the basin a series of more 

 or less gentle undulations. Many of these lines of elevation 

 lift the formations below the coal to the surface, sometimes 

 causing the latter to be washed away over considerable ex- 

 tents of country, thus dividing the region of the large basin 

 into a number of subordinate coal basins. These anticlinal 

 lines sometimes rise into the height of mountainous ridges, 

 called by different names, as Elk Mountain, Chestnut Ridge, 

 Laurel Hill, Negro Mountain, etc. The whole number of 

 these anticlinal axes, or western parallel Appalachian ranges, 



