1921] NATURAL SCIENCES OF PHILADELPHIA 173 



zones of biotite and talc, resulting in the impoverishment of these 

 constituents in the dike which crystallized into an aggregate of 

 oligoclase, corundum, and margarite, with occasional tourmahne. 



Table I. Analysis of Oliogclase. 



A B 



SiO? 61.36 62.76 



AI2O3 22.97 21.95 



CaO 5.38 2.68 



NaoO 8.08 10.31 



K2O 1.08 



H2O 1.72 0.29 



99.51 99.07 



Sp.gr 2.633 2.628 



A. Oligoclase, Spanish Peak, Plumas County, Calif.; Lawson, loc. cit., analysis 

 by J. Newfield. 



B. Oligoclase, Mosso Santa Maria, Biella, Italy; A. Cossa.^^ 



PENNSYLVANIA AND MARYLAND ALBITITES. 



Albitite has long been quarried for feldspar in the serpentine 

 area along the Pennsylvania-Maryland line, which includes south- 

 ern Lancaster and Chester counties, Pennsylvania, and Cecil Coun- 

 ty, Maryland. 



The geology of part of the district has been described by Bas- 

 com,^^ and the principal quarries by Hopkins'' andBastin.^^ 



The district is underlain by an igneous complex, to the north of 

 which lies a mica gneiss thoroughly injected by a fine grained gra- 

 nite. The igneous rocks form a batholithic mass, in which the 

 following interesting series is exhibited in passing from the south- 

 east to the northwestern part of the district: biotite granodiorite, 

 hornblende granodiorite, quartz-biotite-hornblende gabbro, quartz- 

 hornblende gabbro, hornblende-norite and quartz-norite, norite, 

 pyroxenite, and peridotite. All are more or less metamorphosed, 

 the granodiorites assuming a gneissic structure, while the perido- 

 tite is usually altered to serpentine. 



The more important albitite dikes are limited to the largest ser- 

 pentine mass which lies along the Pennsylvania-Maryland line 



^* A. Cossa. Ricerche chimice e microscopiche su roccie e minerali d'ltalia, 

 Feldispathe corindonifero della Biellese. Torino, 1881, 65. 

 '" Maryland Geolog. Survey, Cecil County, 83-148, 1902. 

 i^Ann. Rep. Penna. State College, 1898-99: 7-20. 

 i«U. S. Geol. Surv. Bull. 420: 63-77, 1910. 



