128 



THE CRYSTALLINE ROCKS OF CECIL COUNTY 



CHEMICAL COMPOSITION. 



Norite, three-quarters of a mile northwest of McKinseys Mill. 



Si0 2 48.02 



A1 2 3 20.01 



Fe 2 3 1.13 i 



FeO 7.291 



MgO 10.05 



CaO 11.42 



Na 2 51 



K 2 05 



H 2 + 57 



H 2 0- 10 



C0 2 25 



Ti0 2 23 



Zr0 2 none 



S0 3 undet. 



CI « 



F « 



FeS 2 2 3.H (.06 S.) 



.03 



.01 

 .18 



NiO, CoO 



MnO 



BaO none 



SrO « 



Li 2 trace 



V 2 3 02 



RECALCULATION OF ANALYSIS. 



Orthoclase 28 



Albite molecule 4.35 



Anorthite molecule 52.97 



Hypersthene 39.70 



Magnetite 1.63 



Misc 1.32 



Total 100.25 



Total 



98 



Made by W. F. Hillebrand of the U. S. Geol. Survey. Amer. Geol., 

 vol. xxviii, pp. 151-152. 



THE SOUTHERN GABBRO BELT. 



Grays Hill, east of Elkton, Chestnut Hill and Iron Hill in Dela- 

 ware, and two outlying exposures, one on the Pennsylvania railroad, 

 three-fourths of a mile south of Iron Hill station, the other on the left 

 bank of Big Elk Creek, two miles north of Elkton, exhibit olivine- 

 and hypersthene-gabbro, pyroxenites, peridotites and serpentine. 



1 Subject to correction for influence of possible pyrrhotite. 



2 Sulphur calculated as FeS 2 , but exists as pyrrhotite or other sulphide soluble 

 in HC1. 



3 Perhaps mainly pyrrhotite. 



