NOTES ON THE SERPENTINOUS ROCKS OF ESSEX COUNTY, NEW 

 YORK ; FROM AQUEDUCT SHAFT 26, NEW YORK CITY ; AND FROM 

 NEAR EASTON, PENNSYLVANIA. 



BY 



George P. Merrill, 

 Curator of the Department of Geology. 



A.— ESSEX COUNTY, NEW YORK. 



That the Serpentine of the ophiolite of Thurman, Warren County, 

 New York, was a secondary product after a lime magnesian pyroxene 

 has been stated by the author in a previous paper.* Since that paper 

 was written he has, through the kindness of Prof. J. C. Smock of the 

 State Museum at Albany, had an opportunity for examining similar 

 material from Bolton and Warrensburgh, in Warren County, and from 

 Amity, in Orange County. In all of these the serpentine is plainly of 

 like origin.t It was also stated in the paper mentioned that a part at 

 least of the Essex County serpentine was of like metasomatic origin, 

 but that a considerable portion was apparently after a mineral the 

 exact nature of which had not been determined. Further investiga- 

 tion has not completely solved the problem, but as the matter must be 

 dropped here for the present it is deemed best to put on record such 

 results as have thus far been obtained. As is well known the Essex 

 County ophiolite is the primary limestone of Emmons, and which it will 

 be remembered he considered to be of plutonic origin.J 

 Concerning the composition of the rock this writer says : 

 This range of limestone is distinguished throughout, so far as I am acquainted with 

 it, for its compound character, heiug combined or mixed in several proportions with 

 serpentine. In some parts of the rock the limestone and serpentine are in about 

 equal proportions; iu other instances the limestone predominates, the serpentine 

 gradually disappearing, till only here and there a small portion is discernable, when 



* On the Ophiolite of Thurman, Warren County, New York, with remarks on the 

 Eozoon Canadense. By George P. Merrill, Am. Jour. Sci., xxxvii, March, 1889, p. 189. 



t On account of the known occurrence of chondrodite in the limestone of Orange 

 Couuty it was thought that a portion at least of the serpentine of this locality might 

 result from alteration of this mineral. None of the sections at hand show this to be 

 the case. The altering mineral is in all cases colorless, non-p!eochroic, with well de 

 veloped prismatic cleavage, and is insoluble in acids. Chondrodite, on the other- 

 hand, is pleochroic in yellowish colors and shows only very imperfect cleavages, be- 

 sides gelatinizing when treated with hydrochloric acid. 



JNat. Hist, of New York: Part iv, Geology, p. 228. 



Proceedings National Museum, Vol. XII — No. 783. 



595 



