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. Prom 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 Erie shale, from Ohio through north-western Pennsyl- 

 vania into New York. Fossils were collected and sections taken at a 

 great number of localities along each line. The results of these investi- 

 gations, briefly given, are as follows : 



1st. 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 



