SILICA. 



291 



Fig. 203. 



Fig. 203. 



A fine emerald green coccolite, associated with tabular spar, and quite similar to that of 

 Willsborougli in Esse.\ county, is found in place, and in considerable abundance, about half 

 a mile from the above locality. 



New- York County. Crystallized pyroxene, of the white variety, is very often found in 

 the dolomite of this island. It sometimes has a granular structure like the dolomite, and it 

 not unfrequently is so much charged with carbonate of lime as to effervesce in acids. The 

 crystals heretofore noticed arc eight-sided prisms, with the two opposite sides often much 

 larger than the other six, so as to present a tabulated form represented in Fig. 202. This, 



however, often has I enlarged to the di- 

 mensions of r. Another form is that 

 represented in Fig. 203, in which the 

 lateral primary planes are entirely obli- 

 terated by the new ones r and I ; jxrior- 

 thogone of Haiiy, I on r 90° 0'. The 

 prism is variously terminated, sometimes 

 as in Fig. 201, and at others they are 

 more complex, giving rise to a new va- 

 riety which Haiiy (to whom the speci- 

 mens were sent) named epimeride* Fig. 

 204. M on a; 134° 17' ; i on I 139=" 7' ; r on a? 126° 36' ; a? on ;c 131'-' 8'. Specific gravity 

 3.10. The crystals arc of various sizes, from minute to several inches in length, and they 

 are imbedded in the limestone which crosses the island at its northern extremity, in greater 

 or less abundance throughout its whole extent. The abandoned quarries at Kingsbridge, 

 about 20Sth-street, also afl!"ord very good specimens. 



Oneida County. Large bowlders, made up of coccolite, glassy quartz and tabular spar, 

 are found at Boonville. The coccohte is of a rich green colour, semi-transparent, and is 

 equal in beauty to any in the United States. The specimens closely resemble those which 

 are found in place in Lewis on the borders of Jefferson county, forty or fifty miles north (see 

 Tabular spar, page 271). 



Orange County. The mineral riches of this county arc in no respect more remarkable 

 than in the abundance and variety of pyroxenes which are found in it. If it were possible, it 

 would perhaps be unnecessary, to enumerate all the localities, and I shall therefore confine 

 myself to some of the more interesting ones. And it should here be stated, that we are 

 chiefly indebted to Dr. Horton for what is known concerning these and other minerals of 

 Orange county ; and the reader who desires more particular information concerning them, is 

 referred to that gentleman's Catalogue, published in the New-York Geological Reports of 1S39. 

 The lighter coloured varieties of pyroxene, in this county, are usually found in wJiite lime- 

 stone ; the darker ones are most generally as.sociatcd witli the magnetic iron ore. In many 



■ Troost. Journal of ttu Academy of Natural Scieyices of Pliiladelyhia. Hi. 105. 



