IGNEOUS ROCKS 321 



nia railroad north of Camp hill. Some stray boulders of the rock show 

 on Camp hill, but the dike can not be traced farther into the Paleozoics. 

 The rock is of the same petrographic type as the Conshohocken dike and 

 possesses like structure and constituents. A third dike of considerable 

 width strikes northeast from Mortonville toward Downingtown. 



A very fine-grained diabase dike 8 to 10 centimeters in width and 

 somewhat more basic in composition traverses the Ordovician schists at 

 Williamsons point, on the Susquehanna river. All these dikes are of 

 Triassic age. 



Analyses of material from two diabase dikes 



I. II. 



Si0 2 51.56 50.79 



A1 2 0, .... 17.38 14.19 



Fe 2 3 6.57 3.84 



FeO 3.85 7.44 



MgO 3.42 7.88 



CaO 10.19 9.75 



Na 2 0.. 2.19 1.89 



K 2 1.46 0.95 



Loss 2.15 1.95 



Ti0 2 1.63 0.70 



PO, 0.13 0.15 



Li 2 Trace. Mno. 0.48 



100.53 100.01 



Analysis I is of a diabase dike, West Conshohocken, Montgomery county, 

 Pennsylvania. 



Analysis II is of a diabase dike, Williamsons point, on the Susquehanna river,* 

 Lancaster county, Pennsylvania. 



Norms 



I. II. 



Quartz 13.44 3.36 



Orthoclase 8.90 6.12 



Albite 12.56 16.24 



Anorthite 36.42 26.97 



Enstatite. 8.50 Hypersthene 21.79 



Wollastonite 5.57 Diopside 16.65 



Apatite 0.34 0.34 



Ilmenite 3.04 1.37 



Magnetite 7.89 5.57 



Hematite 1.12 .... 



H 2 2.15 1.95 



* 99.93 100.36 



*Analyses made by Dr F. A. Genth, Jr., Second Geological Survey of Pennsylvania, vols, ccc, 

 p. 27"), and c 6 , p. 134. 



XTJII— Bull. Gf.oi,. Soc. Am., Vol. 1G, 1904 



