362 CHARLES S. PROSSER 



which on fresh surface are generally blue or gray in color, are not 

 very coarse in texture, and the layers are often less than a foot thick. 

 All of these rocks, however, on long exposure usually present along 

 the highways a slightly greenish or yellowish-gray tint. There are 

 two prominent sandstone zones in this member of the formation, 

 varying in thickness from about 30 to 75 feet. The lower one is 

 from 500 to 550 feet above the base of this division, or from 1,000 

 to 1,050 feet above the base of the formation, while the upper zone 

 is at or near the top of the formation. Both of these sandstone zones 

 are clearly shown in the sections on the Williams Road and at Great 

 Cacapon, and the upper one at Gilpin and above Corriganville. The 

 shales in many localities are very fossiliferous, especially those 

 between the two sandstone zones, and contain numerous specimens 

 of such characteristic species of the New York Hamilton as Spirijer 

 mucronatus (Conrad), S. granulosus (Conrad), Athyris spiriferoides 

 (Eaton), Tropidolepius carinatus (Conrad), Chonetes coronatus 

 (Conrad), Phacops rana (Green), and other species. On account 

 of the presence of numerous Hamilton species together with a litho- 

 logic similarity and approximate stratigraphic position, this division 

 of the Romney formation is regarded as equivalent to the Hamilton 

 stage of New York. 



The estimates of the thickness of the Romney formation vary 

 from about 1,600 to 1,650 feet. In Allegany county both the Mar- 

 cellus shale and Hamilton stage are clearly shown; but farther east 

 in Washington county the Marcellus shale or a part of it is wanting. 

 This would indicate that the subsidence of the Onondaga land area 

 began at an earlier date in Allegany than in Washington county. 



CORRELATION OF THE MARCELLUS SHALE. 



The lithological similarity of the thin, black shales forming the 

 lower part of the Romney formation to the Marcellus shale of New 

 York has been noted in the description of the Romney formation, 

 and in other places in the Maryland volume. This is so marked 

 in connection with its similar stratigraphic position that the north- 

 ward continuation of these shales in Bedford county, Pennsylvania, 

 were unhesitatingly called the Marcellus by Professor Stevenson 

 in his geological report of that county. Following the northeasterly 



