/ 



304 F. BASCOM — PIEDMONT DISTRICT OF PENNSYLVANIA 



Analyses of Wissahickon mica-schist and mica- gneiss 



1 



Si0 2 43.81 



A1 2 3 27.52 



Fe 2 3 7.30 



FeO Trace. 



MgO 1.77 



CaO 0.19 



Na 2 0.56 



K a O 8.81 



H 2 + . 

 H 2 — . 

 C0 2 .... 



7.52 



3.78 



Zr0 2 



P 2 5 0.13 



CI 



F 



S 



Cr 2 O s .... 



NO 



MnO 



BaO 



SrO 



Li 2 Trace. 



2 



3 



4 



5 



6 



43.10 



39.35 



56.40 



66.13 



73.68 



30.86 



31.92 



19.76 



15.11 



12.49 



7.28 



2.19 



4.35 



2.52 



2.10 





9.00 



4.40 



3.19 



2.22 



1.80 



3.08 



3.11 



2.42 



2.04 







0.09 



1.87 



0.56 



0.66 



1.98 



5.82 



2.71 



2.97 



6.87 



5.26 



1.27 



2.86 



2.91 



5.91 



6.05 



3.37 



None. 



1.34 



3.28 



1.20 



1.05 



0.82 

 Not estimated 



0.81 



Trace. 



0.49 



0.37 

 Trace. 



0.22 

 Not estimated 

 Not estimated, 



0.03 



None. 



Trace. 



0.12 



.... 



0.06 



.... 



0.20 



Trace. 



Trace. 



0.18 



.... 





Trace. 



None. 





99.76 



100.58 



99.99 



99.87 101.42 



Analyses 1. Mica-schist between Gulf Mills and Hitner's marble quarry. 



Analyses 2. Mica-schist between Gulf Mills and King of Prussia. 



Analyses 3. Mica-schist 1,222 feet from " Bird in Hand " tavern, on road from 

 Gulf Mills to Bryn Mawr. 



Analyses 4. Mica-gneiss, Neshaminy creek. 



Analyses 5. Mica-gneiss. Analysis made from four samples representing four 

 localities. 



Analyses 6. Mica-gneiss, Neshaminy creek, below (4). Analyses 1, 2, 3, 4, and 

 6 made by F. A. Genth, Jr., volume C 6, Second Geological Survey of Pennsyl- 

 vania, pp. 132, 133, 108, 109. Analyses 5 made by W. F. Hillebrand, of the 

 United States Geological Survey. 



Cleavage and fissility are always marked features of the mica-gneiss, 

 but most marked where the formation is least feldspathic and most 

 micaceous. The micaceous variety readily splits into fragments aptly 

 likened by Professor Rogers to " half-rotted fibrous wood." Stratifica- 

 tion is often obscure in the material poor in feldspar, but where fresh 

 rock is exposed bedding can usually be discerned. 



The beds show minute crumpling and both gentle and steep folding 

 (see plate 54). In the latter case cleavage, fissility, and bedding are 



