camibkll] BITUMINOUS COAL FIELD OF PENNSYLVANIA. 27 1 
MONONGAHELA VALLEY. 
Up to the present time six 15-minute quadrangles have been sur- 
veyed in the southwestern part of the State, where the great Pittsburg 
coal bed outcrops. In this territory coal is by far the most important 
economic factor. The area so far snrvej^ed covers nearly the whole 
of the celebrated Connellsville coke field, a portion of the gas coal 
field of the Irwin or Port Royal basin, and much of the territory 
along Monongahela and Youghiogheny rivers, in which the coal is 
mined for fuel only. The determination of the geologic structure in 
this field is of the utmost importance to coal operators, for their mines 
must be developed in accordance with it, and for this purpose alone 
the representation of the structure by means of contour lines is worth 
many times the cost of the work. 
In this part of the field there are a number of coals higher in the 
series than the great Pittsburg bed, but they are not utilized at 
present, and presumably the} 7 will not be until the great coal bed 
beneath them is exhausted. Of these coals the more important are the 
Redstone, lying from 50 to 80 feet above the Pittsburg; the Sewickley, 
at about 120 feet, and the Waynesburg coal, at from 330 to 400 feet. 
The last-mentioned coal is the thickest bed above the Pittsburg hori- 
zon, but it is generally so full of impurities that its value is not so 
great as that of some of the smaller beds. 
Below the Pittsburg coal there are several beds of coal in the Alle- 
gheny measures, but they probably will not be utilized until the 
better coal is exhausted. The most important of these beds is the 
Upper Freerjort, which lies at the top of the Allegheny formation. 
Along the west foot of Chestnut Ridge this bed attains a great aggre- 
gate thickness, but it is so badly broken by shale partings that it is 
expensive to mine, and the fuel when mined is of inferior quality. 
Associated witli the coal beds of the Allegheny formation are some 
valuable deposits of fire clay, which are being worked to some extent 
along the Youghiogheny River and on Chestnut Ridge. These clays 
are highly refractory and of great importance in the coke regions, 
where the consumption of fire brick in the building of ovens is 
enormous. 
The territory surveyed in Monongahela Vallej 7 includes two or three 
prominent gas fields and a few very small pools of oil. The largest 
gas fields are located along the crest of the Bellevernon or Waynes- 
burg anticline. They have two points of development — one near 
Waynesburg, in Greene County, and the other where 1 he axis crosses 
the Monongahela River near Bellevernon. A small but very produc- 
tive field has lately been developed upon the Fayette anticline in 
Fayette County, just west of Uniontown. These gas fields a re usually 
found upon the crests of the anticlines, and it is possible that they 
may be extended along the axial lines. The highest point of the Fay- 
ette anticline, near Jacobs Creek, has never been tested by the drill, 
