Utica Slate and 



thickness, and contain characteristic fossils of the Hudson River 

 formation above the Utica slate, namely: Amhonychia radiata, 

 Modiolopsis modlolaris, Cyrtolites ornatus^ etc. The extensive de- 

 velopment of this portion of the group in the valleys of the Black, 

 Salmon and Hudson rivers, and its almost entire absence near Utica, 

 is undoubtedly owing to some local cause which affected the distri- 

 bution of the coarser sediments. 



The Utica slate formation was traced by the New York geologists 

 down the Mohawk valley from Oneida county through Herkimer, 

 Montgomery, Schenectady and Saratoga counties to the shores of the 

 Hudson. At Baker's Falls, Saratoga county, it is seen in contact 

 with, and resting upon, the Trenton limestone. It here contains 

 graptolites characteristic of the formation in Central New York and 

 also the typical fossil of this horizon, Triarthrus JBechi. Trilobitic 

 remains are very rare in localities where graptolites abound in the 

 undisturbed slates in Oneida county. This is particularly noticeable 

 in the graptolitic slates of the Hudson River valley, where the 

 graptolitic fauna flourished to the almost entire exclusion of other 

 forms common to the slates elsewhere. 



Prof. Wm. W. Mather ' gives the following localities in the 

 Hudson river valley below Baker's Falls, where the Utica slate is 

 to be observed with its characteristic graptolites; at Waterford, 

 Cohoes, Norman's kill below Albany, at Hudson, and also one and 

 one-half miles below on the same side of the river; in the black 

 slate of the Shawangunk mountain, one and one-half miles east of 

 EUenville, Orange county; also at Blue Rock in Marlborough on the 

 bank of the Hudson several miles below Poughkeepsie.'- Owing to 

 the disturbed condition of the strata the graptolites afford the means 

 of determining the geological horizon, where, without their being 

 present, it would be exceedingly difficult if not impossible to do so. 



Prof. R. P. Whitfield, in a letter^^ written to Dr. C. A. White, 

 gives a very full description of the occurrence of the graptolites at 

 Norman's kill and the evidence they afforded of the equivalency of 

 the graptolitic slates and the Utica slate. 



Prof. Mather included a greater range of rocks in the Hudson 

 River group, on the east side of the Hudson, than is now recognized 

 as belonging to it. The evidence, however, that he adduced in 1843 



1 Geol. ofN. Y. Surv. First Oeolog. Dist., pp. 393-395. 1843. 



^ It is interesting to note in tliis connection that Mr. T. Nelson Dale, Jr., has 

 recently discovered typical Hudson River group fossils in this same vicinity. 

 Amer. Journ. Sci. Arts, xvii, p. 57. 1879. 



3 WJieeler Expd. West of the imh Meridian, iv, Pt. I, Pal., p. 19. 1875. 



