GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE 59 



by overthrust upon the slate (see plate 9) and occasionally the 

 limestone outcrops along the slope to the northeast for a short 

 distance. 



Terranes present. The Potsdam, Beekmantown (Calciferous- 

 Rochdale group) and Trenton horizons have been identified along 

 this central strip within the quadrangle. 



The Potsdam. This horizon was first noted in this strip just 

 a little north of the quadrangle boundary half way between Pleasant 

 Valley and Salt Point.^ At Pleasant Valley Lingulepis pin- 

 n i f o r m i s was reported along or near the western margin of the 

 strip to the northwest of the village in rather characteristic argil- 

 laceous limestone, and also from some hills to the north of the vil- 

 lage between the old Poughkeepsie and Eastern Railroad bed and 

 Wappinger creek.^ At the latter place the beds carrying L. p i n n i - 

 f o r m i s also had small brachiopods, apparently Orthis and Tri- 

 plecia, as well as minute gastropods, fragments of trilobites and 

 Ophileta compacta. These beds were mixed with Calci- 

 ferous and Trenton strata carrying other fossils characteristic of 

 tliese limestones in this region. The Potsdam was identified near 

 Rochdale, just west of the Poughkeepsie-Pleasant Valley road. The 

 beds exposed in the quarry just northwest of Alson De Garmo's 

 house, from which stone was removed for the State road, are pos- 

 sibly of Upper Cambric age. A search for fossils in this quarry 

 was unrewarded. In a note to his paper on the discovery of Pots- 

 dam fossils in Poughkeepsie, south of the driving park, as described 

 for the western strip. Professor Dwight' mentioned the discovery 

 of a fragment of brachiopod shell which he believed to be that of 

 Lingulepis pinniformis in a rock very similar to that 

 at the locality south of the driving park. Pie described this new 

 locality as about one-half of a mile south of the Boardman mansion 

 on the Spackenkill road, but it is uncertain from his description at 

 just what point the fossil was found. 



The Beekmantown (Calciferous-Rochdale group). In Jan- 

 uary 1880, Professor Dwight* reported the discovery of a rich 

 assemblage of fossils of Pretrenton age at Rochdale, a small fac- 

 tory hamlet four miles northeast of Poughkeepsie. 



iW. B. Dwight. Amer. Jour. Sci., July, 1881, 34:27-32. 



2 (W. B. Dwight) J. M. Clarke. Guide to the Fossihferous Rocks of 

 New York State. N. Y. State Mus. Handbook 15, p. 9-10. 



3 Amer. Jour. Sci., Feb. 1886, 31:136. 



* Arner. Jour. Sci., January, 1880, 19 :50 et seq. 



