GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 6 1 



taurifrons and B. crotalifrons). New cephalopod species 

 were described as Cyrtoceras vassarina, C. ? dacty- 

 loides, C. microscopicum, Orthoceras apissi- 

 septum; O. henrietta, Oncoceras vassiforme. 



In 1900 Dwight^ designated the main Calciferous strata as the 

 Cyrtoceras vassarina beds and called attention to the great 

 persistence for a distance of nearly thirty miles in the Wapping:er 

 limestone, of a layer which contains a fauna quite different from 

 that of the main beds. It lacked cephalopods entirely. There were 

 no important fossils in common in the two beds except two or three 

 always present in the Calciferous. In some respects it resembled 

 the Fort Cassin of Vermont, but differed in the extreme scarcity of 

 cephalopods. The presence of Lingulepis pinniformis 

 suggested a low horizon in the Calciferous. What D wight has called 

 a low horizon in the Calciferous may be Upper Cambric discon- 

 formably overlain by Beekmantown. 



The Trenton. Fossils belonging to this horizon were the first 

 to be discovered in the Dutchess county limestone 'u.nd were tirst 

 reported from the area within this quadrangle. 



Mather referred only in a footnote to their having been found in 

 a quarry south of Pleasant Valley by Professor Briggs. His assign- 

 ment of the age of this formation was based on fossils found in 

 the beds of limestone within the slate formation a mile or so north 

 of Barnegate. 



In 1879 Professor Dwight- found the following Trenton fossils 

 at Rochdale : Leptaena (Plectambonites) sericea, 

 Orth'is tricenaria, Receptaculites sp. A week after 

 the discovery Dwight and Dana visited this locality. The following 

 fossils were found: L. (P) sericea, Eschar aporarect a, 

 Ptilodictya acuta, the caudal shield of a trilobite probably 

 Asaph us vetustus, Orthis tricenaria, O. pec- 

 tinella, O. t e s t u d i n a r i a, an Endoceras, an Orthoceras, 

 specimens of Chaetetes, and encrinal columns.^ On this same excur- 

 sion the quarry south of Pleasant ValLey, mentioned by Mather, 

 was visited. A fossil assemblage very like that at Rochdale was 

 at once discovered. Subsequent examination of this collection 

 showed Strophomena alternata fragments. The 

 Chaetetes was named by Dwight C. tenuissima. 



1 Bui. Geol. Soc. Amer., v. 12, 1900, abstract. 



2Amer. Jour. Sci., May, 1879, 17:389. 



3 Amer. Jour. Sci., May, 1879, 17:390. See also p. 381. 



