WESTERN COUNTIES OP PENNSYLVANIA 6^ 



in by far the greater part of the count}^. These do not extend into Craw- 

 ford, but disappear northwardly at about 3 miles south from the line of 

 that county. Iron ore is associated with both limestones, sometimes 

 even replaces them. Both beds contain familiar Coal Measure fossils. 

 A coal bed underlies each limestone, and at one locality near the Venango 

 line there is an intermediate bed at 6 feet above the Lower Mercer lime- 

 stone. These are the Alton beds of Ashburner. 



The Upper Connoquenessing sandstone is from 40 to 60 feet thick, 

 light gray, and pebbly near the top. The Lower Connoquenessing is 

 from 30 to 89 feet, varying abruptly and for the most part at the expense 

 of the Sharon shales. The Quakertown shales show the coal bed in the 

 upper portion and vary from 20 to 50 feet. The Sharon shales are 

 usually less than 30 feet, but where the overlying sandstone is thin they 

 become 70 feet and show thin coals at 65, 50 to 45, and 22 feet above the 

 Sharon coal bed. The last attains its chief importance in this county, 

 but its occurrence is very uncertain, as the coal is in pots or saucer- 

 shaped deposits which are largest and carry the best coal on the Ohio 

 side of the county, where the thickness is sometimes 5 feet. 



The Sharon sandstone is diminishing southwardly, for it is only 20 

 feet thick at Sharon, and it disappears somewhere in the southern part 

 of the county. Along the Ohio border it shows the usual features, but 

 eastward it is for the most part only a massive sandstone, at times be- 

 coming flaggy* 



In Lawrence county, south from Mercer, the Homewood sandstone, 

 about 40 feet thick, varies from sandstone to shale. It is a sandstone 

 near the Mercer line, as also in the southern tier of townships bordering 

 upon Beaver county, but in a great part of the county it is apparently 

 shale. At never more than 5 feet below this sandstone is the Tionesta 

 coal bed of I. C. White, which appears to be at the horizon of the Mount 

 Savage coal bed. It extends northward almost to the Mercer line and 

 appears to be persistent, since wherever its place is exposed one finds 

 either a bed of impure coal or a deposit of very black bituminous shales. 



The Mercer group shows in by far the greater part of the county the 

 two limestones and coal beds. The Upper Mercer limestone, as in Mercer 

 county, is much more variable than the Lower, and not infrequently is 

 represented only by its ore bed.- Both limestones are present in all of 

 the townships along the Ohio line, and notable variation appears only 

 as one approaches the Butler county line at the east ; yet both are 

 present in the extreme southeast corner of the county. 



The Connoquenessing sandstones are as variable as the Homewood. 



* I. C White : Geology of Mercer County (Q3), 1880, pp. 33-58. 



