On the Mineralogy of New York Island, 187 



having that substance incrnsting and imbedded in the surface 

 of the mica, giving it the appearance of mingled burnished 

 and frosted silver work. A black rhomboidal mica, from the 

 vicinity of 57th street, precisely resembles that from Brevig, 

 Norway. The same neighborhood has also furnished firm, 

 small, but perfect, crystals of Muscovite. 



Among the enclosed minerals of our micas, afe flattened 

 crystals of quarts, garnet, kyanite, and other crystals of mica, 

 in which the planes or axes lie at nearly all angles with those 

 of the larger plates in which they are imbedded, and from 

 which they are easily detached, affording an instance of dis- 

 tinct crystals imbedded in larger crystals, or in massive speci- 

 mens of the same mineral. 



The optical character of our micas seems not to have been 

 made the subject of examination as yet. 



In the coarse granite of 2d avenue, near 42d street, large 

 crystalline masses of feldspar abound, varying in color from 

 greenish-white, through flesh color and red, to a peculiar dark 

 brown, much resembling the perthite from Canada. 



Occasionally, large and perfect crystals, presenting the faces 

 of a hexedral prism with two terminal planes, furnish speci- 

 mens worthy a place in the cabinet. 



In some instances the colored feldspar produces a handsome 

 red granite, although the masses are usually too large, and the 

 accompanying quartz and mica too limited in quantity to make 

 a good building granite. 



Near 50th street, the kaolin resulting from the decomposi- 

 tion of feldspar is so fine, that when wet it feels as smooth and 

 soft as tallow, but falling to powder when dry. It often occurs 

 in the same rock with the unaltered feldspar. 



Garnets are abundant in many places, and in some speci* 

 mens from 42d street,, the crystals were as large and perfect, 

 and of as good color as those from any American locality. But 

 few of them were found, and these were imbedded in veins of 

 gray quartz from the gneiss rock. The form is the trapezohe- 



NOVEMBER, 186& 14 Ann. Lyo. Nat. Hist., Vol. VIII. 



