86 GEOLOGY OF OHIO. 
to 400 feet in thickness, forming the summit of the Devonian system. 
Above the Catskill are the Vespertine sandstones and Umbral shales; 
then the Conglomerate and Coal Measures. From Tioga county Mr. Sher- 
wood worked westward, carefully tracing these various formations until 
his observations connected with those made by Mr. G. K. Gilbert and 
myself, who went eastward from the Ohio line, and met him in McKean 
county, Pennsylvania. At the same time my assistants, Messrs. Hooker 
and Potter, carried similar lines of observation at a lower level, along the 
outcrops of the Hrie shale, from Ohio through north-western Pennsyl- 
vania into New York. Fossils were collected and sections taken at a 
ereat number of localities along each line. The results of these investi- 
gations, briefly given, are as follows: 
Ist. The Chemung group forms the summit of the series in Cha- 
tauqua county, New York, there attaining a thickness of nearly 2,000 
feet. It includes the Conglomerate seen at the “ Panama rocks,” formerly 
regarded as the Carboniferous conglomerate—at least 160 feet below the 
summit of the series; as it is overlaid by that thickness of shales contain- 
ing unmistakable Chemung fossils. The Chemung group, in all this 
region, is highly arenaceous, containing many beds of sandstone, nearly 
al of which are, in some localities, conglomerates. The various sand- 
stones reached in the oil wells, on Oil Creek, are parts of this formation, 
and all apparently contain more or less pebbles. Coming westward into 
Ohio, the Chemung rocks rapidly diminish in thickness, and become 
more argillaceous in character. They form the greater part of the Erie 
shale, in its exposures between Ashtabula and Cleveland. 
2d. The Catskill group constitutes a well-defined and strongly marked 
geological formation in Bradford, Tioga, and Potter counties, Pennsylva- 
nia, where it has a thickness of several hundred feet; has very distinct 
lithological characters, and contains in great abundance the remains of 
fishes, such as are found in no other formation on the continent. Of these 
the most abundant are the scales of Holoptychius and the plates of Both- 
riolepis. In coming westward, the Catskill formation rapidly thins, and 
apparently disappears before the Ohio line is reached. 
3d. The Vespertine sandstones of Rogers, which have a thickness of 
more than a thousand feet in central Pennsylvania, are there nearly des- 
titute of fossils. In tracing this formation towards the west, it was found 
to diminish in volume, and to become finer and more argillaceous in 
texture. It still remains, however, as a reddish sandstone, dark or light, 
with alternating beds of shale at Bradford, in McKean county, and in the 
valley of the Alleghany, near Kinzua. Lower down on the Alleghany, 
and in the valley of Oil Creek, it forms that portion of the section which 
