116 



THE CRYSTALLINE ROCKS OF CECIL COUNTY 

 CHEMICAL ANALYSES OF MICA-GNEISS. 





Ii 



II 



III 



IV 



V 



VI 



VII 



Si0 2 



66.13 



66.42 



60.33 



61.96 



57.66 



58.37 



64.20 



A1 2 3 



15.11 



14.76 



20 . 85 



19.73 



22.83 



21.99 



16.80 



Fe 2 3 

 FeO 



2.52 

 3.19 



7.50 



3.59 



4.47 



4.60 



7.74 



10.66 



4.23 



MgO 



2.42 



1.80 



2.07 



1.81 



3.56 



1.20 



3 . 94 



CaO 



1.87 



2.22 



1.82 



.35 



1.16 



.30 



.73 



Na o 



2.71 



1.75 



1.38 



.79 



.60 



trace 



3.07 



K 2 



2.86 



3.52 



2.84 



2.50 



5.72 



1.93 



3.26 



H 2 + 

 H 2 0— 



1.55) 



.24 } 



1.85 



2.78 



1.82 



1.50 



4.03 



3.42 



Ti0 2 



.82 





1.41 



1.66 





trace 





Zr0 2 



no test 

















co 2 



none 













.39 





p 2 o 5 



.29 





.28 







.93 





s 



trace 











.11 





Cr 2 3 



none 

















NiO 



trace 



















MnO 



.22 







trace 



trace 



trace 







BaO 



( faint \ 

 \ trace [ 

















SrO 



none 















Li 2 



j faint ) 

 ( trace j 





..... 











Total 



99.93 



99.82 



101.82 



99.55 



100.77 



99.91 



99.65 



I. — Sample material from several representative localities in Philadelphia belt of 

 mica-gneiss. Analysis made by W. F. Hillebrand in the laboratory of the IT. S. 

 Geological Survey. 



II.— Biotite gneiss, Freiberg, Saxony. Described as containing orthoclase, plagio- 

 clase, quartz, biotite, more or less muscovite, and apatite, rutile, zircon, tourmaline, 

 garnet, hornblende and pyrite as accessory constituents. Zirkel, Lehrb. Petro., 

 vol. iii, p. 223. 



III. — From exposure north of Jenkintown Junction and west side of Tacomy 

 Creek. F. A. Genth, Jr., Analyst. Described as containing garnet, mica, feldspar 

 and magnetite. Report C 6 ., p. 122. 



IV. — Gneiss from St. Jean de Matha, Province of Quebec. A quartzitic gneiss 

 with orthoclase, garnet, sillimanite, graphite and pyrite. N. N. Evans of McGill 

 University, Analyst. F. D. Adams, Amer. Jour. Sci., July 1895, p. 67. 



V. — Gneiss from the west shore of Trembling Lake, Province of Quebec, 

 tite gneiss with quartz and orthoclase and bands of garnet and sillimanite 

 Adams of McGill University, Analyst. F. D. Adams, loc. cit. 



VI. — Peach Bottom roofing slate from Harford County. Booth, Garrett and Blair, 

 Analysts. See Md. Geol. Surv., vol. ii, p. 226. 



VII. — Roofing slate (Cambrian) from Melbourne, Province of Quebec. T. Sterry 

 Hunt, Analyst. Geology of Canada, 1863, p. 600. 



A bio- 

 W. C. 



Iron oxides uncorrected for influence of sulphides or vanadium. 



