1894. 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



639 



in the quartz porphyries and liparites, but such as I have never seen 

 in rocks so basic in composition as is this. 



Under a power of 390 diameters the individual cohimnsof tlie aggre- 

 gate were found in some instances to be almost Avliolly without action 

 or polarized light, or again i)olarized in light and dark colors, some of 

 the better defined giving extinctions parallel with or ranging but a few 

 degrees from the axis of greatest elongation, and eminently suggestive 

 of feldspars; in a few instances indetinite interference figures were 

 obtained, but only such as might be due to tensile strain on isometric 

 or amorphous bodies. 



The results of purely o^itical investigation proving thus unsatisfac- 

 tory, an attempt was made at a separation of the mineral by pulveriza- 

 tion and pic«ipitation in the iodide of mercury and jiotash solution. 



This proved a work of great difificulty, owing to inclusions of iron 

 ore and the chloritic alteration which had set in. After repeated 

 attempts a powder coming down at a density of 2.5G was obtained in 

 sufficient quantity for analysis. This yielded Mr. Eakins, of the U. S. 

 Geological Survey, results as follows: 



SiO. 



Al,()3 



Fc.O, 

 CaO' 

 MgO 

 K,0. 



H,0. 



Such a composition is evidently that of a mixture, and maj' perhaps 

 be explained on the assumption tliat it consists of two feldspars (sani- 

 dni and a soda-lime variety) and an aluminous pyroxene. 



The pyroxenic constituent, as above noted, occurs both in por])hyritic 

 forms and as a constituent of the groundniass, sometimes in good idio- 

 morphic forms and again as rounded and irregular granules scattered 

 singly and in clustered aggregates. Except in the matter of size the 

 individuals of the two generations are indistinguishable from one 

 another, are of a light greenish color, not noticeably pleochroic, and 

 give extinction angles on clinopinacoidal sections as high as 41^. The 

 larger porphyritic forms are sometimes 3 or 4 mm. in diameter, while 

 those of the groundniass are, as a rule, not over 0.05 mm., and at times 

 sink to 0.02 mm. 



By pulverization and separation by the iodide of n)ercury and potash 

 solution, and subsequent digestion in hydrochloric acid and potassic 

 carbonate, a sufficient supi)ly of the pryoxenic constituent was obtained 

 for a complete analysis. This, submitted to jVIr. Eakins, yielded results 

 as given in column i, below. In columns ii, iii, and iv are given for 



