walcott.] GEORGIA TERRANE. Ill 



Washington County, New York, which includes green and purple slates, 

 were of the same geologic age as the Georgia slate. 1 



The extension of the " Granular Quartz " of the eastern part of New 

 York into Dutchess County was described by Dr. W. W. Mather 2 as it 

 occurred about Stissing Mountain. He refers„to it as the " Granular 

 Quartz " and Potsdam sandstone. Within a few years Prof. John C. 

 Smock 3 examined the geological structure of the mountain, stating 

 that the quartzite was unconformably superjacent to the Archean 

 rocks; and that no fossils had been found in it. In the description of 

 the Primordial rocks of the Wappinger Valley, by Prof. W. B. Dwight, 4 

 mention is made of the quartzite about Stissing Mountain, as well as 

 the discovery by himself and Mr. C. D. Walcott of Middle 5 Cambrian 

 remains in the arenaceous quartzite and limestones on the flanks of the 

 mountain. It is thus correlated with the Olenellus beds of the Georgia 

 scries of Vermont. 



At the Ann Arbor meeting of the American Association for the 

 Advancement of Science, held in August, 1885, Prof. Dwight 6 an- 

 nounced the discovery of fossiliferous Potsdam strata at Poughkeepsie, 

 New York. He says 7 : 



Lithologically, the rock is here very variable. It is everywhere calcareous, all its 

 varieties effervescing freely with acids. It is also everywhere more or less arena- 

 ceous, often conspicuously so ; from being compact and massive it changes to a rock 

 fissile into thin slabs or to one splitting into the thiunest leaves, which are covered 

 with loose sand as they decompose. 



This rock passes on the one hand into a smooth fine-grained, argillaceous limestone, 

 and then into a very fissile calcareous shale or, on the other hand, into a quartzite, 

 somewhat calcareous. 



An account of the localities at which the rock occurs and a list of 

 eleven species of fossils are given. This paper was published more in de- 

 tail in the number of the American Journal of Science for February, 

 .1886, and was accompanied b5 r a map on which the geographic distribu- 

 tion of the Potsdam and related strata are shown. 8 



Prof. Dwight 9 announced in 1889 the discovery of fossiliferous strata 



1 Walcott, C. D. Cambrian age of the roofing slates of Granville, Washington County, New York. 

 Am. Assoc, Proa, vol. 35, 1887, pp. 220, 221. (Advance sheets published 1886.) 



* Natural Hist, of New York. Part 1. Geology of New York; Geology of the first (southeastern) 

 district, Albany, 1843, pp. 418, 423, 436, 437. 



3 A geological reconnoissance in the crystalline rock region, Dutchess, Putnam, and Westchester 

 Counties, New York. Thirty-ninth Ann. Peep. State Mus. Nat. Hist., 1886. pp. 166-185. 



4 Primordial rocks of the Wappinger Valley limestones and associated strata, Vassar Brothers 

 Inst., Trans, vol. 4, 1887, pp. 206-214. Discovery of additional fossiliferous Potsdam strata and pre- 

 Potsuam strata of tho Olenellus group uear Poughkeepsie, N. Y Am. Jour. Sci., 3d ser., vol. 34, 1887, 

 pp. 27-32. 



5 Now classed as Lower Cambrian. 



■Discovery of fossiliferous Potsdam strata at Poughkeepsie, N. Y., Am. Assoc. Proa, vol 34, 1886, 

 pp. 201-209. 



7 0p.cit.,p. 205. 



"Recent explorations in the Wappinger Valley limestone of Dutchess County, N. Y.,No. 5. Dis- 

 covery of fossiliferous Potsdam strata at Poughkeepsie, N. Y. (illustrated by map, Plate vi). Am. 

 Jour. Sci., 3d ser., vol. 31, 1886, pp. 125-133. Primordial rocks of the Wappinger Valley limestones 

 Vassar Brothers' Inst. Trans., vol. 4, 1887, pp. 130-141, Plate 1. 



9 Recent explorations in the Wappinger Valley limestones and other formations of Dutchess County, 

 N. Y. Am. Jour. Sci., 3d ser., vol. 38, 1889, pp. 139-153. 



