220 



Report of the State Geologist. 



GONi f L US ION. 



On the geologic map accompanying this report, the boundaries of the 

 Hamilton formation, and the Sherburne and Ithaca formations taken together 

 are given for Chenango, Otsego, Schoharie, Albany and Greene counties. In 

 the preceding portion of this report detailed sections with lists of fossils are 

 given for Chenango and Otsego counties. It was intended to give a similar 

 account of the investigation in Schoharie, Albany and Greene counties, but 

 the pressure of other duties renders it necessary to defer their description until 

 a later date, when a summary of the more important facts brought out by this 

 investigation Avill appear. However, in order that the reader may apprehend 

 the more important changes advocated in the present report, it is thought best 

 to state them briefly. 



On comparison it will be noticed that the line marking the upper 

 boundary of the Hamilton formation on the geologic map is from five to fifteen 

 miles farther south than the similar line on the geologic map, recently pub- 

 lished by the Geological Survey of the State of New York. 1 



As stated in the introductory part of this paper, wherever the Tully lime- 

 stone is found, it affords a sharp line of separation between the Hamilton and 

 Chemung series ; but in eastern and eastern central New York the Tully 

 limestone as well as the overlying black Genesee slate has disappeared and 

 there is a more gradual passage from the Hamilton to the Chemung series. 

 The author began work in De Ruyter, Madison county, where both the Tully 

 limestone and Genesee slates occur, and followed those formations into the 

 Chenango valley, where they disappear. In Onondaga, Cortland, Madison 

 and Chenango counties, above the Tully limestone and Genesee slate, are the 

 thin bluish sandstones and smooth shales of the lower Portage of central and 

 western New York. Vanuxem proposed the name "Sherburne flagstone" 2 

 for this formation, which has been adopted in this report, and it is shown to 

 have a thickness of 250 feet in the Chenango valley. In this valley and 

 the westward the Sherburne formation contains comparatively few fossils, 

 though to the east, after the disappearance of the Tully limestone and 

 Genesee slates, the number of species, particularly of Hamilton forms, 

 increases, as has been shown in the latter part of this report in describing the 

 exposures in the eastern part of Otsego county. However, when the sections 

 are carefully studied by one familiar with the Hamilton and Chemung series, 



1 Preliminary Geologic Map of New York, exhibiting the structure of the State 80 far as known Prepared under the direc- 

 liun of James Hall, Slate Geologist, by W. J. McGee. Published by aulhority of the Legislature of the State of New York. 

 Printed by the United States Geological Survey, 18!tl (distributed April, 1896). 



'' Fourth Annual Report, Third Geological District (Assembly Document No. 60, 1840), p. .'181. 



