312 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



generally, however, there is a tinge of green or olive pervading these strata. Toward the upper 

 part of the group, in many places, there is a tendency to conglomerate; and in a few localities 

 the mass becomes a well-characterized puddingstone, stiU retaining the fossils of the shales 

 and sandstones. This conglomerate nowhere attains sufficient thickness or importance to merit 

 a distinct description, but in hasty observations it may sometimes lead to erroneous inferences, 

 since it resembles in many respects the distinct and well-defined conglomerate which rests upon 

 this group in the western part of the State, but which is totally distinct from the same. 



Many of the shaly sandstones and shales of this group are highly micaceous, and toward 

 the upper part of the whole the shales are reddish, coarse, and fissile, with much mica in small 

 glimmering scales. There is also in these shales a slight change in the character of the prevailing 

 organic forms. 



Two observers, Prosser and Williams, have specially studied the Chemung and 

 also the earlier Devonian. Prosser ''^^'^ described in great detail the sections of 

 the strata in south central and eastern New York, and in his later report he 

 concludes :^^^'' 



Succeeding the TuUy hmestone and Genesee slate, or farther east, where these formations 

 have disappeared, the Hamilton formation, is a mass of thin bluish sandstones and smooth shales 

 of Portage age, for which Vanuxem proposed the name "Sherburne flagstone," which has been 

 adopted and used as the name for the formation. It has a thickness of 250 feet in the Chenango 

 Valley and may be readily traced westward to the meridian of Cayuga Lake, west of which 

 Prof. J. M. Clarke has shown that it gradually passes into the Naples beds. Eastward from the 

 Chenango Valley the Sherburne formation crosses Chenango, Otsego, and Schoharie counties, 

 entering Albany County, where it turns south-southwesterly, and apparently extends to the 

 Delaware River crossing Greene, Ulster, Sulhvan, and Orange counties. Where the Sherburne 

 formation is separated from the Hamilton by the TuUy hmestone and Genesee slate, fossils 

 are comparatively rare in it, but to the east of the Chenango VaUey, in Otsego and Schoharie 

 counties, they are more common and constitute a modified Hamilton fauna. In eastern New 

 York across Greene and Ulster counties the upper part of the flagstones or "North River 

 blue stone" is apparently in the Sherburne formation but contains scarcely any fossils except 

 occasionally a few species of plants. 



Above the Sherburne is the Ithaca formation, which has a thickness of 500 feet in the 

 Chenango Valley and extends from the vicinity of Keuka Lake, where it has been shown by 

 Prof. Clarke that the "Portage or Naples fauna prevails largely to the exclusion of representa- 

 tives of the Ithaca fauna,"" eastward across Schuyler, Tompkins, Cortland, Chenango, Otsego, 

 and Schoharie counties. In eastern New York across Albany, Greene, Ulster, and Sulhvan 

 counties the physical conditions which existed during the deposition of the Oneonta and Catskill 

 formations appear to have also prevailed during Ithaca time and perhaps they began in the 

 Sherburne, so that there is very little evidence of the Ithaca fauna, the fossiliferous bluish and 

 grayish shales of the more western counties being replaced by the unfossihf erous red and greenish 

 shales and sandstones. In Orange County and northeastern Pennsylvania there is some 

 representation of the Ithaca fauna, the reds appearing later as one follows this series to the 

 southwest. Prof. Clarke has clearly shown that the Ithaca fauna in the Chenango Valley is 

 composed of "a more abundant representation of unmodified Hamilton species" than in the 

 Ithaca region,'' which is also true to the east of the Chenango Valley, as demonstrated by the 

 numerous lists of fossils given in this report. 



From the Chenango Valley eastward the Ithaca is capped by the Oneonta formation, which 

 is composed of red and green shales, reddish sandstones, and coarse-grained grayish to greenish- 



" Fifteenth Ann. Rept. New York State Geologist, p. 81 and "Geological map showing the distribution of the 

 Portage group." 



6 Idem, pp. 46-63. 



