640 STOSE AND LEWIS TBIASSIC IGNEOUS ROCKS 



constitution, as illustrated by the examples in the following table. It is 

 to be regretted that none of the rocks of this immediate district have 

 been analyzed ; but the following analyses from other areas are given here 

 as a suggestion of the variations that probably occur in the rocks of the 

 Gettysburg area. No analyses of the extreme quartz-orthoclase types — 

 aplite and micropegmatite — are available from any part of the region. 

 These would undoubtedly show much higher silica and alkalies and lower 

 lime, iron, and magnesia than any of the examples quoted here. 



Analyses of various Types of Triassic Diabase 3 



12 3 4 5 6 7 



Si0 2 60.05 56.78 51.68 46.87 55.31 50.88 49.02 



A1 2 3 11-88 14.33 15.87 13.36 13.64 13.17 10.14 



Fe 2 3 3.22 5.76 1.46 9.79 0.52 1.11 1.54 



FeO 10.21 9.27 8.43 2.71 8.49 9.66 10.46 



MgO 0.85 1.58 7. 84 4.35 12.73 13.05 17.25 



CaO 4.76 5.26 11.08 14.70 12.41 10.19 8.29 



Na 2 4.04 3.43 1.86 4.64 1.40 1.17 1.59 



K 2 2.10 1.75 0.34 2.01 0.32 0.31 0.40 



H 2 0+ 0.66 0.10 0.15 0.14 0.59 



H 2 0— 0.21 0.33 0.16 0.16 



Ti0 2 1.74 1.44 0.72 1.9S tr. 0.99 



P 2 5 0.52 0.36 0.12 tr. 0.11 



MnO 0.28 0.25 0.15 tr. tr. 0.16 



100.52 100.64 99.86 100.41 100.82 99.67 100.70 

 Sp.gr 2.872 3.152 



1. Quartz diabase (dacose, II. 4. 2. 4). Pennsylvania Railroad tunnel through 

 the Palisades, 400 feet from the west portal, Homestead, New Jersey. 



2. Quartz diabase (tonalose, II. 4. 3. 4). About 420 feet from the upper sur- 

 face of the sheet, Rocky Hill, New Jersey. 



3. Diabase (auvergnose, III. 5. 4. 3). Rocky Ridge, Maryland. 



4. Diabase (kilauose, III. 5. 2. 4). Birdsboro, near Norristown, Pennsylvania. 



5. Hypersthene diabase (auvergnose, III. 5. 4. 3). The Twins, Culpeper 

 County, Virginia. 



6. Olivine-hypersthene diabase (auvergnose, III. 5. 4. 3). The Twins, Cul- 

 peper County, Virginia. 



7. Olivine diabase (palisadose, IV. I 2 . I 2 . 2). The Palisades, Englewood 

 Cliffs, New Jersey. 



3 Numbers 1 and 7, by R. B. Gage (Ann. Rept. Geol. Survey of New Jersey for 1907, 

 p. 121) ; 2, by A. H. Phillips (Amer. Jour. Sci., vol. viii, 1899, p. 267) ; 3, by A. E. 

 Schneider (Bull. U. S. Geol. Survey, No. 148, p. 90) ; 4, by H. Fleck (19th Ann. Rept. 

 U. S. Geol. Survey, vol. vi, cont., p. 222) ; 5 and 6, by W. G. Brown (Bull. Geol. Soc. 

 Am., vol. 2, 1898. p. 34G). 



