J. J. Stevenson— Upper Devonian Rocks of Pennsylvania. 427 
Catskill or Chemung, or to represent both groups, unless indeed 
those have thinned out. Professor H. D. Rogers thus describes 
the Chemung and Catskill of Pennsylvania :— 
‘““VERGENT SERIES. 
“Vercent Fiacs (Portage flags of New York).—A rather 
fine-grained gray sandstone in thin layers, parted by thin 
alternating bands of shale. It abounds in marine vegetation. 
Thickness in Huntingdon 1,700 feet. 
“VERGENT SHALES (Chemung group of New York),.—A thick 
mass of gray, blue and olive-colored shales, and gray and 
brown sandstones. The sandstones predominate in the upper 
part, where the shales contain many fossils. Thickness in 
Huntingdon 3,200 feet. 
‘‘ PONENT SERIES. 
“Ponent Rev SANDSTONE (Catskill group of New York).— 
In its fullest development this is a mass of very thick alternat- 
ing red shales with red and gray argillaceous sandstones. It 
has very few organic remains. Among them is oloptychius, 
and one or two other remarkable fossil fishes, of genera dis- 
tinetive of Old Red Sandstone. This formation has its maxi- 
mum thickness in its southeastern outcrops, where it measures 
more than 5,000 feet.”—Final Rep. First Geol. Surv. Penn., 
vol. 1, p. 108. 
On pages 140, 141 and 142 of the same volume, Professor 
Rogers gives some further details respecting the lithological 
characters of the rocks. In the northwest belt, the Vergent or 
Portage flags consist of dark gray flaggy sandstones parted by 
thin layers of blue shale, with large marine plants and a 
Nucula as the chief fossils, while in the next belt toward the 
west they are made up of thin-bedded, fine-grained, siliceous 
gray sandstones, intimately alternating with blue and greenish 
shales, 
In the middle belt, the Vergent Shales or the Chemung con- 
sists of gray, red to olive sandy shales, with gray and red 
argillaceous sandstones, but no details are given respecting this 
“aie in the belts west or northwest from the Alleghany 
ountains. : 
In the northwest belt, the Ponent or Catskill consists of fine 
and argillaceous sandstones, with an increase of red and green 
shale and with some calcareous layers. 
On page 798 of vol. ii of the same report, Professor Rogers 
points out the similarity between the deposits of the Ponent 
and Vergent, and states that the sediments of the former are 
quite as impalpable as are those of the latter. 
all these descriptions ~be compared with those already 
given of the rocks occurring in the gaps of the Youghiogheny 
