124 



THE CRYSTALLINE ROCKS OF CECIL COUNTY 



CHEMICAL COMPOSITION. 



I. II. III. 



Si0 2 58.57 55.16 44.04 



A1 2 3 . ... 16.10 17.51 20.01 



Fe 2 3 2.89 2.62 4.221 



FeO 6.12 5.83 8.61 



MgO '. 2.33 4.35 5.01 



CaO 7.39 8.50 11.68 



Na 2 2.11 1.83 1.24 



K 2 1.01 1.08 .15 



H 2 + 1.27 2.01 1.90 



H 2 0- 21 .21 .11 



C0 2 none none none 



TiOo 1.41 .64 2.24 



ZrO„ 09 .02 .10 



P 2 0~ 37 .21 .52 



P0 3 undet. undet. nndet. 



CI none " " 



F nndet. " " 



FeS 2 2 trace .03 3 (.02 S.) .25 (.135 S.) 



Cr 2 3 none trace none 



NiO CoO " .01 .01 



MnO 18 .15 .28 



BaO trace trace none 



SrO , 



Li 2 " " trace 



V 2 3 02 (.018) .04 (.036) .05 (.053) 



Total 100.07 100.17 100.42 



I. — Quartz-biotite-hornblende-gabbro. Near the Foundry on Stone Run. 



II. — Quartz-biotite-hornblende-gabbro. Near Porter Bridge on Octoraro Creek. 



III. — Hornblende-gabbro. Stone Run, % mile northwest of Rising Sun. 



Analyses made by W. F. Hillebrand in the laboratory of the United States 

 Geological Survey. Amer. Geol., vol. xxviii, p. 146. 



RECALCULATION OF ANALYSES I 



I. II. 



Quartz 21.56 10.33 



Orthoclase 6.12 6.42 



Albite molecule 17.90 15.76 



Anorthite molecule 18.96 16.73 



Hornblende 19.76 27.05 



Biotite 8.70 18.61 



Magnetite 4.18 3.77 



Apatite 81 .45 



Misc 1.91 1.10 



99.90 



100. 



III. 



1.39 



.89 



10.53 



44.61 



30.79 



8.33 



4 8.33 5 



1.14 



2.70 



100.38 



1 Subject to correction for influence of possible pyrrhotite. 



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

 in HC1. 



3 Perhaps mainly pyrrhotite. 

 * Titaniferous. 



5 The percentage of magnetite is probably unduly large because of the uncorrected 

 ferric oxide percentage. 



