MONONGAHELA FOEMATION 33 



Ligonier, Connellsville, and Lisbon, in which it retains a good thick- 

 ness to the last exposure, but farther west the diminution is more 

 marked, for in northern Allegheny the bed rarely exceeds 4 feet 6 inches, 

 while in Beaver county it falls to 3 feet 6 inches; but in Jefferson of 

 Ohio it is 4 feet at the most northerly exposure. The conditions along 

 the northwestern and western outcrop are suggestive. The greater 

 thickness in Jefferson and the marked increase to 6 feet southwest in 

 Harrison county makes the greatly increased thickness, 8 to 9 feet, 

 in western Morgan and Athens not at all surprising. It is clear that 

 the thin coal of Guernsey is only evidence of approach toward the bar- 

 ren area, which begins in the southern part of that county. The west- 

 ern limit of the bed must have been considerably west from the present 

 outcrop in Harrison, Guernsey, and Muskingum; it is probable that a 

 great area of thick coal has been removed, and that the thick coal of 

 Morgan at one time covered most of Muskingum and Carroll counties, 

 west from Guernsey and Harrison. The great thickness at the extreme 

 northern exposures within the Ligonier, Connellsville, and Lisbon basins 

 leads to the belief that Professor J. P. Lesley was not far wrong when 

 he suggested that the Pittsburg at one time reached almost to lake Erie. 



While the bed loses thickness from all sides toward the central area, 

 where it is wanting or so insignificant as to be unimportant, it is equally 

 true, as already stated, that even within that area one finds patches in 

 which the bed is of commercial importance. One of them, with Pome- 

 roy, Ohio, as its chief shipping point, has an area of not far from 100 

 square miles; those along the Kanawha in West Virginia are smaller, 

 but there the bed shows at times its complex "roof," "over-clay" and 

 "Main" coal, with the latter exhibiting close structural resemblance to 

 typical localities near the Pennsylvania line. Such occurrences are of 

 great interest from the theoretical standpoint. 



In some portions of the field the Pittsburg coal bed shows a tendency 

 to wide separation of parts, somewhat like that observed in the anthra- 

 cite beds and in the Pottsville beds of the Kanawha region. In the 

 Potomac basins of Maryland and West Virginia the several portions 

 of the bed are separated by shales and clays, so as to occupy a vertical 

 space of 40 to 63 feet; in the Salisbury basin of Pennsylvania the bed 

 and its partings are in a vertical space of 46 feet at the southern end, 

 but this increases to about 160 feet at the northern end, with shales, 

 sandstones, and limestones in the intervals; in the Connellsville basin 

 one finds at a few miles south from Uniontown, in Payette county, the 

 Pittsburg in all about 14 feet thick and 30 feet below the Eedstone coal 

 bed; but northward the Pittsburg interval quickly increases to 58, 66, 



