424 CHARLES S. PROSSER 



the top of the formation, as shown in the Cumberland and 

 Pennsylvania R. R. cut east of Barrelville, is a greenish zone five 

 feet thick composed partly of sandstone and partly of a calcare- 

 ous breccia containing clay pebbles. The thickness of the for- 

 mation is 650 feet. In the lower part of the shales and along 

 the Greenbrier— Mauch Chunk contact are numerous excellent 

 springs. The formation is named from Mauch Chunk in eastern 

 Pennsylvania and is the Canaan formation of the Piedmont folio. 

 The Greenbrier limestone and Mauch Chunk shales taken 

 together are known as No. XI of the Pennsylvania reports. 



Pottsville formation. — The preceding three formations are 

 usually grouped together as the sub-Carboniferous or Lower 

 Carboniferous, and the Pottsville is classed as the oldest of the 

 Carboniferous proper or Upper Carboniferous formations. It 

 crosses the county from Pennsylvania to the Potomac, in general 

 forming the crest line of Alleghany Front although in the north- 

 ern part it is lower, and extends up the Potomac valley to above 

 Westernport. At .numerous places near the crest line of Alle- 

 ghany Front it forms conspicuous cliffs. It also occurs at the 

 northwestern corner of the county. The formation is composed 

 of massive light gray sandstones with some conglomerate strata 

 and thin-bedded gray sandstones and shales. Some of the 

 shales are black and there are several thin beds of coal. The 

 most important are first, the Bloomington, which is exposed along 

 the Baltimore and Ohio Railroad west of Piedmont, W. Va., 

 commonly known as the Railroad seam, varying in thickness 

 from less than two to more than three feet and occurring about 

 150 feet below the top of the formation. The second is the 

 Westernport seam about two feet thick which occurs below the 

 Homewood sandstone near the top of the formation. Some of 

 the sandstones are suitable for building stone. The thickness is 

 estimated as between 450 and 500 feet and there are fragments 

 of fossil plants. The formation is named from the exposures of 

 massive conglomerate in the vicinity of Pottsville in eastern 

 Pennsylvania. It is the Blackwater formation of the Piedmont 

 folio and No. XII of the Pennsylvania reports. 



