OF DENISON UNIVERSITY. 7 



ions Portage, Chemung and Catskill, and finds that the Catskill period 

 presents a closely circumscribed area during the deposition of the last 

 beds of the Chemung but was greatly enlarged to the southward dur- 

 ing the formation of its upper beds. We incline to this opinion, at 

 the same time correllating the Chemung of Brown county N. Y. , 

 with part of Mather's Catskill group of the Catskill mountains as Mr. 

 N. H. Darton has done, leaving the Catskill group of Stevenson as a 

 formation which had its greatest and typical development south of the 

 Pennsylvania line, and outside of the typical locality which includes 

 strata not understood when Mather made the survey of his district. 

 It may be that the red Bedford shale lying at the base of the Waverly 

 formation in Ohio represents a connection with the Catskill of the 

 east about the latitude of Pittsburg, but it contains recurrent Hamil- 

 ton species which lingered in the west long after the Hamilton forma- 

 tion was succeeded by later deposits in New York. The Bedford sea 

 could probably be represented as an estuary in Ohio, which was 

 bounded on the west by the fold of Cincinnati rocks and those of 

 later age. The gradual uplifting of northern Ohio which had then 

 begun, continued in operation until the following lower Carboniferous 

 horizons were deposited on a shoreline which steadily progressed 

 southward. 



The Chemung group is 350 feet thick in southwesthern Virginia 

 on the Tennessee line, but rapidly thickens northward, being 3800 

 feet thick on the boundary line between Virginia and Pennsylvania, 

 4700 feet in Huntington county Pennsylvania, and four thousand feet 

 near the New York line on the Delaware river, while in the Catskill 

 mountains it is 3000 feet thick. In southwestern New York the Che- 

 mung is 1200 feet thick. The Chemung strata thin out to the west- 

 ward and south-westward in Pennsylvania, but northward along the 

 western boundary line it reaches a thickness of 1400 feet in Crawford 

 county near Lake Erie. The Erie shales which represent the western 

 extension of the Chemung in Ohio rapidly thin out as we approach 

 Columbus, almost, if not quite disappearing as we approach that city. 

 Prof. E. Orton states its thickness at 300 feet, but it is very vari- 

 able. When the stratigraphy is subject to so much variation in thick- 

 ness, lithological appearance, and distribution, we must be prepared 

 to be somewhat at variance concerning the origin of its individual 

 beds of conglomerates, as well as the remaining strata. Prof. I. C. 

 White has correllated the Panama with the Alegrippus conglomerate, 



