Campbell] BITUMINOUS COAL FIELD OF PENNSYLVANIA. 273 
cipal anticlinal folds show some extensive fields of gas. The exten- 
sions of these fields are always along the crest of the anticlines, and 
the gas men soon found that the folds as previously mapped are incor- 
rect. Instead of coming to the conclusion that the gas fields bear no 
relation to the structure, they at once satisfied themselves that the 
previous determination of the structure was inaccurate. 
The areal mapping of the territory shows conclusively that the gas 
men are correct in their conclusions, and that when the structure of 
the oil field is correctly represented it is entirely in harmony with the 
location of the oil pools. 
One of the most pronounced changes in the interpretation of this 
region is in what was formerly called the Bradys Bend anticline. 
This was supposed to cross the river at the mouth of Redbank Creek 
and to extend in a straight line along a course about north 35° E. 
The present work shows that the location of this anticline near the 
Butler County line is correct, but instead of crossing the river at the 
mouth of Redbank Creek it swings sharply to the east and crosses 
the river just above the mouth of Mahoning Creek, corresponding at 
that point with the anticline formerly known as the Kellersburg, and 
extending across Redbank Creek on the line formerly supposed to 
represent Anthonys Bend anticline. In other words, the anticlines 
formerly designated Bradys Bend, Kellersburg, and Anthonys Bend 
are all on the same fold. The synclinal basin west of Bradys Bend 
anticline shows a corresponding swing to the east and agrees approx- 
imately with the Lawsonham syncline, as previously determined. 
The abrupt bend in this synclinal basin gives strikes nearly east and 
west in the vicinity of Bradys Bend and also nearly north and south 
on the Butler County line. This is in perfect agreement with the 
trend of the oil pools in this region, and is conclusive proof that when 
the structure is well understood it may be used as a guide in extend- 
ing oil operations. 
The Fairmount syncline was fairly well determined in previous sur- 
veys, except that in the vicinity of Mahoning Creek it bifurcates and 
the right branch swings to the east along the creek and replaces what 
was formerly called the Leechburg syncline. This change has no 
direct effect on any economic product, but it shows that the previous 
determination of straight axes is very misleading. 
The most important change in the eastern part of Armstrong County 
is in the anticline which lies next east to the Fairmount syncline. In 
previous work this had been broken up and received different names; 
along Crooked Creek and Kiskiminitas River it was known as the 
Bagdad anticline, while on Pine and Mahoning creeks it was called 
Greendale anticline. These two folds are now known to be continuous, 
and instead of extending in a straight line to the northeast after 
crossing Pine Creek, it swings sharply to the right in harmony with 
Bull. 213—03 18 
