EELATIOX TO OTHER COAL AREAS. 43 



Armstrong, Jefferson, Elk, Cameron, Potter and Tioga counties, the most 

 northerly exposure of coal being on Driftwood creek in the last-named 

 county. 



The fifth basin is bounded at the west by the Brady's Bend anticlinal, 

 wdiich is persistent to the northern line of the state. It embraces por- 

 tions of Allegheny, Armstrong and Clarion counties, and crosses southeast 

 McKean into Potter county, where the Coal Measures appear in small 

 areas of insignificant value. 



The sixth basin embraces the rest of northwest Pennsylvania, and may 

 be regarded as including all that remains of the bituminous region in 

 Pennsylvania and Ohio, for bej^ond the Brad3^'s Bend axis the folds are 

 petty and without great extent along the strike. 



RELATION TO MARYLAND AND VIRGINIA COAL AREAS. 



Practically, the last four basins become one at the south. Certainly 

 the third and fourth may be regarded as one at but a little way south- 

 ward l^eyond the A\"est Virginia line, while at 50 miles south from the 

 Baltimore and Ohio railroad, in that state, the first and second have 

 coalesced with each other and with the third, owing to the steady de- 

 pression of the anticlinals in that direction. So, then, what are the con- 

 ditions in these basins ? 



Along a line drawn from central Ohio eastwardly through southern 

 Pennsylvania to the Cumberland coal basin, one finds gentle dips, rarely 

 exceeding one or two degrees, until the Coke basin is reached at, say, 50 

 miles southeast from Pittsburg, where they become steeper, reaching 4° 

 or 5° in the bottom of the trough, and becoming 10° to 12° on the side 

 of the Chestnut hill anticlinal. Eastward no material change in rate of 

 dip is found until beyond the Alleghany mountain, the westward dip in 

 that monoclinal seldom exceeding 10°. To all intents and purposes, the 

 dips in the first and second bituminous basins, as well as in the first sub- 

 division of the third, are the same ; the last, however, the most westerly, 

 shows a higher dip in the bottom of the trough than is seen in the others. 

 But in the strip between the Alleghany and the North or Kittatinny 

 mountain the folds are numerous, often bold anticlinals cut into mono- 

 clinals, sliowing Lower Silurian or even Cambrian rocks in the inter- 

 vening valleys, while still further toward the Blue ridge, in the Great 

 valley, inverted folds are by no means rare. 



Extent of Deformation of the several Coal Basins. 



If, however, one study the conditions on either side of this line he 

 will find that it is by no means representative of the conditions for any 

 extended area north or south from it. Northward, in all of the basins 



