92 THE MOUNTAIN. 



northeast to southwest, a distance of some seven hundred 

 and forty miles, presenting a width of sometimes one hun- 

 dred and eighty miles. One estimate of its superficial area 

 gives sixty-three thousand square miles. Its original limits, 

 as suggested by geologists, must have measured, before they 

 were reduced by denudation, nine hundred miles in length, 

 and two hundred miles in breadth. 



In the State of Pennsylvania, from its southern line in 

 Somerset county, to the north branch of the Susquehanna 

 River in Luzerne county, the Alleghany Mountain forms 

 the eastern margin of this basin. Between that limit and 

 the State of New York on the north, and Lake Erie on the 

 northwest, all the rocks belong to three or four formations, 

 as already described, including the carboniferous group. 

 The two large formations that underlie the silicious masses 

 under the coal series, the olive slate group, and the red sand- 

 stone and slate group, run along with and form the south- 

 eastern escarpment of the Alleghany Mountain and the 

 range of hills at its base, between the points designated, 

 and sweep in a wide curve around the northeastern termi- 

 nations of the upper rocks in Susquehanna and Bradford 

 counties, and are traceable, although thinning down, west- 

 ward, in a long belt nearly parallel with the north line of the 

 State from Towanda into the State of Ohio. Immediately 

 within the belt thus traced, there is found a bold escarpment, 

 formed of hard sandstones, conglomerates, and silicious 

 slates, directly underlying and forming part of the carbon- 

 iferous formation, which is the actual northeastern margin 

 $f the great bituminous coal basin. The anthracite and 

 semi-bituminous coals are found in the more disturbed and 

 broken belt of the Appalachian range, east of the basin thus 

 designated, but occupying the same geological position ; in 

 other words, being true geological equivalents. The Alle- 

 ghany Mountain, as an individual chain, is the rim, margin, 

 or eastern escarpment of the crops of the sands, conglome- 

 rates, and slates of this vast basin, presenting many flexures, 

 but all with general southwest line of trend. The summits 



