GNEISS 



149 



amorplious carbonaceous matter and little needles of a mineral 

 assumed to be mica. A slate from Hanover, in the same state, 

 contained garnets and staurolites. Wicliman found slates from 

 Lake Superior to consist of a colorless, isotropic ground-mass 

 carrying quartz and feldspar particles, scales of iron oxide, car- 

 bonaceous matter, minute tourmalines, and mica fragments, 

 while T. Nelson Dale has described the roofing slate of western 

 Vermont and eastern New York as composed of quarts, a little 

 plagioclase feldspar, muscovite, chlorite, the carbonates of lime, 

 magnesia and iron, zircon, rutile and pyrite. The chemical com- 

 position of the slates is given on p. 119. 



Chemical Composition. — As may be readily imagined, the 

 schists vary indefinitely in composition. The table given below 

 is intended to show the composition of a few characteristic types 

 only. All gradations, from the most acid of quartzites to the 

 most basic of the amphibolites, may readily be found. 



Chemical Composition of Quartzites and Schists 



Constituents 



Silica (Si02) . . . 

 Alumina (AlaOs) . 

 Ferric oxide (FesOs) 

 Ferrous oxide (FeO) 

 Lime (CaO) . . 

 Magnesia (MgO) 

 Potash (K2O) 

 Soda (NagO) , . 

 Ignition. . . . 



82.38% 

 11.84 



2.28 



1.00 

 0.83 

 0.38 

 0.77 



99.48% 



II 



49.00 % 

 23.65 

 8.07 



« * ■ • 



0.63 

 0.94 

 9.11 

 1.76 

 3.41 



96.56% 



III 



52.39 % 

 16.33 

 1.64 



8.76 

 4.70 

 1.42 

 2.69 

 0.17 



Oy.TcTk jQ 



IV 



49.18% 



16.09 



12.90 



10.59 

 6.22 

 1.51 

 3.64 

 1.87 



100.00% 



V 



50.81 % 

 4.53 

 3.52 

 4.26 



31.55 



4.42 



99.09% 



YI 



97.1 % 

 1.39 

 1.25 



0.18 

 0.13 



100.05% 



I. Miea sctist: Monte Eosa, Switzerland. II. Sericite scMst: Wisconsin. 

 III. Hornblende scHst: Grand Bapids, Wisconsin. IV. CHorite schist: 

 Ellippe, Sweden. V. Talc scMst: Gastein, Austria. YI. Quartzite: CMckies 

 Station, Pennsylvania. All analyses quoted from J. P. Kemp's Handbook 

 of Eocks, 1904. 



