Portage Stages of Ne w Yo rk. 217 



central ]S~ew York to central Pennsylvania and traced the con- 

 tinuation of the different zones, so that he feels inclined to 

 speak with considerable positiveness in reference to this por- 

 tion of the New York Upper Devonian. Moreover, since a new 

 geologic map of New York is in process of coloration, it seems 

 that attention should be called to the correlation of this particu- 

 lar part of the series. Indeed, most of the statements that have 

 been made during the last ten years as to the age of these rocks 

 are not so accurate as the conclusions of Vanuxem over fifty 

 years ago ; so that if this area be colored on the new map, as 

 one would infer from these occasional statements, the map for 

 that section of the State will not be so accurate as the one of 

 1813. These remarks apply especially to that part of the 

 geologic column which in western central JN"ew York extends 

 from the Genesee shale to the base of the Chemung, while for 

 central and eastern New York and Pennsylvania from the 

 Marcellus shale to above the lower reds and grays, called the 

 Oneonta sandstone, as high as marine fossils have been found. 

 Our reason for differing from the ordinary statements in 

 reference to the age of the rocks immediately underlying the 

 Oneonta sandstones (which compose the Oneonta group of 

 Conrad) will be much more clearly understood if we consider 

 first a section like that of Cayuga lake, where the Tully lime- 

 stone and Genesee shale are present in their fall development, 

 and consequently where there can be no question as to the 

 upper limit of the Hamilton stage as originally defined and 

 generally understood and accepted. The bluffs along Cayuga 

 lake and the exposures south of Ithaca, which have been care- 

 fully studied and fully described by Dr. H. S. Williams in 

 various publications, afford such a section.* Along the shores 

 of Cayuga lake are exposed 1,000 feet of argillaceous shales and 

 sandstones containing an abundant and typical Hamilton fauna. 

 Capping the Hamilton is the Tully limestone varying from 15 to 

 rather more than 20 feet in thickness. This is overlaid by the 

 Genesee shale, a very fissile, black, argillaceous shale 100 feet 

 in thickness in this region which in some of the glens, as Bur- 

 dick's, is capped by a prominent sandstone nearly four feet in 

 thickness. The sandstone marks the beginning of the Portage, 

 the lower division of which is composed of sandstone and 

 shales containing but few fossils with a thickness of 250 feet.f 

 Succeeding this division is the " Ithaca group " of Yanuxem, 

 or the middle Portage of Professor Williams, with a thickness of 



*See particularly Bull. U. S. Geol. Surrey, No 3, 1884 ; also Science, vol. i, 

 old series, Oct. 16, 1880, p. 190, Proc. Am. Assoc. Adv. Sci., vol. xxx, p. 1, of 

 reprint, and ibid., vol. xxxiv. p. 222. 



fThis part constitutes the entire Portage of the Cayuga lake region as de- 

 scribed bv Professors Hall and Vanuxem iu their final reports. See Geol. N. Y., 

 Pt. IV, p. 250. and ibid.. Pt. Ill, p. 17 4. 



