512 NEW YORK STATE MUSEUM 



white beds, Hudson shales, Hudson red and green slates and 

 Hudson thin quartzite. The Hudson grit (graywacke) is inter- 

 bedded in many places with black shales or slates, which in a 

 great number of localities furnished the typical NoTmans kill 

 graptoiite fauna (identified by K. K. Gurley). Many of these lo- 

 calities had been found by C. D. Walcott. These graptoiite shales 

 are not only closely connected with the Hudson grite, as the writer 

 found them alsoi to' be at south Troy (Poesten kill, see p. 539) and 

 near East Greenbush, but also with the green and red slates; for 

 " at several points the Hudson grits appear to^ be replaced along 

 the strike by the red and green Ordovician slate " (p. 189). 



The Trenton limestone (p. 190) occurs only sporadically within 

 the lower Siluric areas. " In some places it was probably de- 

 posited contemporaneously with the Hudson grits and shales, or 

 it may underlie portions of them. In others it may represent the 

 entire Lower Silurian series and should then be regarded as 

 Trenton, Chazy and Calciferous." 



This correlation of the Trenton limestone and the Hudson river 

 beds is also expressed in the table of formations (p. 178), where 

 it is said: ^^ Trenton limestone: Limestone, occurring mostly 

 west of the slate belt, replacing probably I (Hudson grits, red and 

 green slate and graptoiite shales), H (Hudson white beds and 

 Hudson thin quartzite) and G (Hudson shales), and possibly F 

 (Calciferous) and then representing the Trenton, Chazy and Oal- 

 ciferous." 



RESULT OF FORMER INVESTIGATIONS. 



A brief retrospect of the opinions expressed by the various 

 authors on the Normans kill fauna will show that there has been 

 a decided trend in these opinions toward a correlation of the Nor- 

 mans kill zone with deeper and deeper terranes till now it os- 

 cillates, so to say, about the lower Trenton. This correlation is 

 based entirely on paleontologic evidence and, as Dr Gurley's con- 

 cise statement clearly shows, is hardly more than tentative. This, 

 however, can not be surprising, when it is borne in mind, that 

 all the graptoiite beds in New York, notably those at Normans 

 kill, the Abbey (Glenmont), Schodack Landing^ Kinderhook and 



