THE CAMBRIC DICTYONEMA FAUNA 

 IN THE SLATE BELT OF EASTERN NEW YORK 



BY RUDOLF RUEDEMANN 



Introduction 



With the progress of the investigation of the thick masses of 

 shales, slates and flags, extending to the east and south of the 

 great St Lawrence and Hudson river valleys from Gasp6 to 

 southern New York, or to the east of " Logan's line," it becomes 

 more and more apparent, that Lapworth exhibited a prophet's 

 intuition in predicting many years ago, that this mass, generally 

 lumped together as Quebec and Hudson river groups, would be 

 found to represent, formation by formation, the more or less cal- 

 careous series to the west and north of that line, from the Pots- 

 dam below to the Lorraine above. 



In the last report of the state paleontologist the writer an- 

 nounced the discovery of three different graptolite zones, ex- 

 posed at the Deep kill in Rensselaer county, which represent the 

 Phyllograptus-Tetragraptus shales of northern Europe and 

 Canada, From their identification with the Point Levis shales of 

 Canada and by correlation with the corresponding zones of 

 Europe, they are placed in the lowest Lower Siluric, and con- 

 sidered as representing the shaly development of the Beekman- 

 town limestone and perhaps also of the Chazy limestone. 



The continuation of the investigation of the slates of Rensse- 

 laer county has this year led, at Schaghticoke on the Hoosick 

 river, to the finding of an outcrop of slates which contain a 

 fauna known from the northeast of this continent and from 

 Europe, and there considered as marking the closing stage of 

 Cambric time. A very large quantity of excellently preserved 

 material has been secured, the graptolitic part of which will be 

 described in a forthcoming memoir. In this report, it is pro- 

 posed to discuss only the geologic aspect of the discovery. 



Description of locality and beds 



The outcrop extends from the bridge of the Mechanicville- 

 Johnsonville branch of the Fitchburg railroad, on both sides of 

 the gorge for about one half mile. The river is forced, in this 



