38 J. J. STEVENSON CAKBONIFEROUS OF APPALACHIAN BASIN 



in all 24 feet 2 inches. A section in Wheeling shows the Upper Se- 

 wickley 3 feet thick and 17 feet above the Lower Sewickley, also 3 feet, 

 a vertical space of 23 feet; but at another place in Wheeling, Doctor 

 White found the three beds once more and in a vertical space of 43 

 feet. At 12 or 14 miles below Wheeling, on the Ohio, Doctor White's 

 section shows the Upper Sewickley 2 feet thick and separated by 12 

 feet of Sewickley sandstone from 10 feet of coal and shale apparently 

 representing the Lower Sewickley. The varying interval between Up- 

 per Sewickley and Pittsburg along the western outcrop suggests similar 

 irregularities in that region. 



The Great limestone (H. D. Eogers, 1858) included all of the lime- 

 stone bed in the Monongahela formation. In 1876 J. J. Stevenson 

 restricted this term to the deposits between the Upper Sewickley and 

 the Uniontown coal beds, and divided it into Lower and Upper ; in 

 1877 he applied the term Uniontown to the upper division, and in 1903 

 Doctor White designated the lower division as the Benwood. 



The Benwood limestone (I. C. White, 1903) is almost directly above 

 the Upper Sewickley coal bed. It seems to be wanting east from the 

 Alleghenies and is very thin along the northern outcrop in Pennsyl- 

 vania, though some trace remains in the Ligonier, Connellsville, and 

 Lisbon basins almost to the last exposure. Farther west in Allegheny 

 and northwest Washington it is either wanting or very thin. South- 

 ward it comes into the section rather abruptly, attaining great thiclcaess 

 almost at once. It is not always continuous limestone, but sometimes is 

 very largely calcareous shale, and at others is broken by shale or sand- 

 stone beds. It reaches its maximum thickness in Fayette and West- 

 moreland within the Lisbon basin, and retains it along the Monongahela 

 river in much of Greene and southern Washington. It is from 60 to 

 90 feet thick in that area and in some places is continuous with the 

 Uniontown limestone above. This great thickness continues for a little 

 way into West Virginia, but it quickly becomes insignificant, and in less 

 than 40 miles there is barely as much as 7 feet in this interval. It 

 seems probable that the mass persists under Greene county of Pennsyl- 

 vania, for where the rocks come up again near the Ohio river it is very 

 thick and so prominent that the name is given from Benwood 4 miles 

 below Wheeling. 



In Ohio this limestone is wanting within northern Jefferson, Harri- 

 son, and northern Guernsey counties; it is thick in eastern Belmont and 

 southern Jefferson, but in the western part of the former county it is 

 broken into many layers, varying in thickness and separated by shales 

 or sandstones. The Benwood interval contains limestone beds along 



