102 J. J. STEVENSON CARBONIFEROUS OF APPALACHIAN BASIN 



erly exposure of its place in Allegheny coTinty, but it quickly increases 

 in northern Washington to 10 and to 30 feet. Unlike the Lower Wash- 

 ington, this deposit is insignificant in the central part of Washington 

 county, where it is represented only by thin streaks ; but it becomes better 

 characterized in the southern part, where, as in Greene county, it is 3 to 

 4 feet thick. It disappears quickly west and south from the Pennsyl- 

 vania line and it cannot be recognized certainly in any of the sections. 

 It may be represented by one of the red beds. A black shale overlies 

 this limestone at many places, and at times is rich in well preserved re- 

 mains of fish. The Blacksville limestone was mistaken for the Middle 

 Washington at several places in Allegheny and northern Westmoreland. 



The Middle Washington limestone (J. J. Stevenson, 1876), numbered 

 IV in volume K of the Pennsylvania reports, is not exposed in Pennsyl- 

 vania east from the Monongahela river, where in all probability it is 

 wanting. A limestone in Maryland has been correlated with this. The 

 Middle Washington is present in most of Washington county, where its 

 variations are very like those of the Blacksville, but its thickness is 

 greater in a larger area; it practically disappears soon after passing into 

 Greene county, and farther south it has been recognized only near the 

 West Virginia border. There it is extremely sandy and weathers like 

 sandstone; but it may be present in this condition elsewhere in the 

 county. Unlike the Blacksville, this is always impure and often fer- 

 ruginous. 



The Franklin limestone (V of Stevenson, 1876) is exceedingly char- 

 acteristic in Greene county, where it is coarsely brecciated and very hard, 

 resisting the weather. It was mistaken by Stevenson for the Upper 

 Washington in northwest part of the county where the higher limestone 

 is very thin. This limestone, rarely more than 3 feet thick and often 

 much less, is from 20 to 35 feet below the Upper Washington in Greene, 

 where it is present at all localities exposing its place; it is present in the 

 western townships of Washington at about 30 feet below the Upper 

 Washington and its thickness exceeds 3 feet only twice. It was not seen 

 in place in the central or eastern parts of the county, but its characteristic 

 fragments were found in Franklin and Amwell townships very close to 

 its proper position. It seems to be absent west from these Pennsylvania 

 counties and Doctor White does not report it from West .Virginia at the 

 south. 



The Upper Washington limestone (J. J. Stevenson, 1876), numbered 

 VI, is the most persistent and in many respects the most striking member 

 of this group. Its northernmost exposure is in northwest Washington 



