GEOLOGY — RESULTS OF CHEMICAL ANALYSES. 77 



c. Special gravity, 2.3242 ; finely granular ; hard ; is composed of alternate layers, one of 

 gray color, the other of pinkish hue ; does not cleave along the apparent strata, but has an 

 irregular fracture. 



COMPOSITION. 



Si. 80.401, Al. 3.145, Fe. 4.061. 

 Ca. 1.365, H. 10.750 = 99.722. 



d. Specific gravity, 2.490 ; extreme change of form ; structure compact, even ; fracture con- 

 choidal, smooth ; color, reddish purple ; resembles jasper. 



COMPOSITION. 



Si. 9G.507, Al. and Fe. 1.181, Ca. .987. 

 Na, trace, H. .546 = 99.507. 



e. Specific gravity, 2.2542. Granular, compact; can be broken with the nail. Color, 

 grayish white. 



COMPOSITION. 



Si. 80.891, Al. 12.211, Fe. 1.771. 

 Ca. 1.181, H. 3.211 = 99.265. 



The next two, M and N, contain silicate of soda, and some iron as protoxide, as is shown by 

 digesting the mineral in fine powder with some hydrochloric acid, and testing with permanga- 

 nate of potassa. 



M. Specific gravity, 2.371. Fracture hackly, coarse. Full of small cavities of a light yellow 

 color. Color of the mass, greenish gray. 



COMPOSITION. 



Si. 69.697, Al. 15.685, Fe. 2.200. 



Ca. .332, Na. 10.00, H. 1.186 = 99.100. 



N. Specific gravity, 2.346. In appearance differs from the last only in haying the cavities 

 in the mass larger and colored darker yellow or red by the sesquioxide of iron. 



COMPOSITION. 



SL 81.540, Al. 8.454, Fe. 4.227. 



Ca. .684, Na. 4.650, H. 1.184 = 100.739. 



The last specimen had a variable composition and appearance. Vitreous opal of a specific 

 gravity 2.105, slightly streaked yellow, by iron constituting central and principal portions of the 

 mass. Surrounding the opal was a brownish substance, P, and outside this a greenish mineral, O. 



O. Specific gravity, 2.392. Coarse, brittle structure ; hard. Fracture irregular. Color 

 greenish. Resembles M in all its properties, physical as well as chemical. 



COMPOSITION. 



Si. 69.455, Al. 12.313, Fe. 2.2QS. 

 Ca. 1.908, Na. 4.667, H. 9.416 = 99.959. 

 P. Specific gravity, 2.4819. Hard and brittle. Color brownish. 



