Raymond: Sections in the Conemaugh Series. 175 



stone, the base of which is almost always noticeably irregular. This 

 unconformity is especially well exhibited along the north bank of the 

 Ohio River from Wood's Run to Dixmont, and on the south bank 

 from Fleming Park to Groveton, Pa. Another place near Pittsburgh 

 where it may be seen and where at least a part of the beds which have 

 been eroded may be determined is on the Baltimore and Ohio Rail- 

 road between Etna and Wittmer, Pa. At Wittmer the section in an 

 abandoned clay pit is as follows : 



lo. Light green clay-shale. Top not seen. 20 ft 20 ft. 



9. Black and dark gray shale with marine fossils in limestone 



nodules, though rarely in the shale itself. 10 ft 30 ft. 



8. Sandy limestone with numerous marine fossils. 8 and 9 are 



the Pine Creek horizon, i ft. 6 in 31 ft. 6 in 



7. Green structureless clay. 10 ft 41ft. 6 in. 



6. One layer sandstone. 2 ft. 6 in 44 ft. 



5. Sandy shales and thin-bedded sandstone. One layer contains 



plant remains and invertebrate fossils. 18 ft. 6 in 62 ft. 6 in. 



4. Thin-bedded gray shale with plant remains. 35 ft. 6 in 98 ft. 



3. Thin-bedded black shale with marine fossils. There is a thin bed 



of impure limestone at the base. Brush Creek horizon. 7 ft. 



6 in 105 ft. 6 in. 



2. Thin-bedded gray shale. Mason horizon. 15 ft. 6 in 121 ft. 



I. Yellow sandstone and shale. 5ft 126 ft. 



The only layers in this section which can be referred to the Buffalo 

 sandstone are those in No. 6 and possibly the upper part of No. 5, 

 certainly not more than 10 feet altogether. Three quarters of a mile 

 south of this point the base of the Buffalo sandstone cuts through the 

 Brush Creek limestone and disappears below the level of the railroad 

 track. Beds 2, 3, 4, and part or all of 5, a thickness of at least 6-8 

 feet, have been eroded away before the sandstone was deposited. 



The period of elevation and erosion was followed by a period of 

 subsidence during which these troughs were filled, possibly by the rivers 

 which cut them. This lowering reached its culmination when the sea 

 again covered the land and the Pine Creek limestone and shale were 

 deposited. In many places the Pine Creek limestone is covered by 

 from 10 to 15 feet of shales containing marine fossils, these shales 

 grading without break into shales with land plants, indicating a prob- 

 able gradual silting up of the sea and the return of land conditions. 

 There was then another elevation which brought the Pine Creek de- 

 posits above sea-level, and valleys were again carved, cutting down 

 into the already consolidated Buffalo sandstone. In these valleys the 

 Cow Run sandstone was deposited, probably by stream action. 



