No. 75.] 141 



Finally, to complete the catalogue of identical minerals, M. Staff 

 states that his analysis of a specimen of sillimanite from Chester, Conn., 

 gives the formula of kyanite, which again is supposed to be identical 

 with the disthene of Haiiy. The recent analyses of Prof. B. Silliman, 

 Jun., also show the identity of sillimanite, bucholzite and fibrolite, with 

 kyanite. Sill. Jour., Nov. 1849. 



If these views are correct, the following minerals should be reduced 

 to one species, viz : 



Bucholzite, Andalusite, 

 Sillimanite, Kyanite, 

 Xenolite, Disthene. 

 Fibrolite, 



Sillimanite has been found in the town of Yorktown, Westchester 

 county, about ten miles north-east of Sing Sing, near the road leading 

 from Pine's bridge to Yorktown post office, associated with monazite, 

 tremolite and magnetic iron. The crystals are distinct and run through 

 the iron ore ; they are often 6 or more inches in length, much bent and 

 fractured, as they are at Norwich and Chester, Conn. {Sill. Jour, xlvi, 

 p. 207.) I have received specimens from my friend, Mr. Cyrus P, 

 Fountain, of Peekskill, 



According to the analysis of Prof. Norton, of Yale College, the 

 Yorktown sillimanite contains, 



SiHca, - - 37-70 



Alumina, - - - - - - - 62 •75 



Oxide of iron, - - - - - - 2*29 



102-74 



{Dana's Mineralogy, 2d ed., p. 378.) 



PITCHSTONE. 



(Mineralogy of New- York, page 367.) 



This is perhaps the most appropriate place for the introduction of a 

 notice of a mineral found by Dr. Emmons at Johnsburg, in Warren 

 county. It is called obsidian, and is described as occurring in a trap 

 dyke at the line of contact of the gneiss, in which it is embraced. 

 The mineral has a bluish black color, a vitreous lustre and a conchoidal 

 fracture. It is only about an inch wide on both sides of the dyke. Dr. 

 Emmons says, *' it is to be considered as a part of the dyke, which for 

 some cause was more perfectly pure, and in consequence of more sud- 



