288 



DESCRIPTIVE MINERALOGY. 



Fig. 193. 



Fig. 19-1. 



M 



I r 



M 



Commencing at the celebrated locality called Rogers' 

 Rock, which rises from Lake George at or very near the 

 line between this and the county of "Warren, we find two 

 or three varieties of this mineral in considerable abun- 

 dance within the compass of a few acres. First, we have 

 a crystallized variety of a greenish grey colour. It occurs 

 in long prisms, which are six and eight-sided by trunca- 

 tions. Yig. 193, pcrihexaedre oi Hauy. Fig. 194, pm- 

 octaedre of Haiiy. M or M' on r 133° 33'; P on r 106° 

 15'; M' on I 136° 15'. One specimen was obtained here, 

 which was between seven and eight inches in length, and of a proportionate diameter. These 

 crystals, which, however, are seldom perfect, are associated with sphene, coccolite and feld- 

 spar. The sphene is sometimes imbedded in various parts of the prism of pyroxene. 



Green, brown and black coccolite are also found at this locality. The grains are of various 

 sizes, and sometimes cohere so slightly that it is difficult to retain specimens of any size. 

 The green variety is less abundant than the others. 



In a crystallized specimen from near Ticonderoga, probably from this locality, Mr. H. Sey- 

 bert found. 



Silica, 52.66 



Lime, 23.33 



Magnesia, 5. 73 



Alumina, 6.66 



Protoxide of iron, 12. 30 



Water, 0.33 



Oxide of manganese, trace.* 



A specimen of coccohte from the same locality, gave Mr. Seybert, 



Silica, 51.00 



Lime, 23.00 



Magnesia, 6. 26 



Alumina, 3. 00 



Protoxide of iron, 14.43 



Water, 0.66 



Oxide of manganese, trace. t 



On Mount Defiance, near Ticonderoga, there is a fine locality of the variety sahlile. Its 

 colours are greyish white and green. It cleaves easily and perfectly in the direction of P ; 

 and its faces of cleavage, w'hich are large, have a high metallic, pearly lustre. It belongs to 

 the variety sometimes called Lamellar pyroxene, and the specimens closely resemble those from 



* Cteavelani's Mineralogy, App. 



t Ibid. 



