180 



PEOCEEDINGS OF THE ACADEMY OF 



[Part I 



and biotite, lost practically everything but the constituents of al- 

 bite, and consequently solidified to a rock consisting almost wholly 

 of this mineral. 



Fig. 9. — Generalized diagram of the contact phenomena shown by the Penn- 

 sylvania and Maryland albitite dikes. Ab = albite; V = vermiculite (alter- 

 ed biotite); A = actinolite, with more or less talc; T = talc; Sp — serpentine. 



Table 3. Analysis of Jefferisite, Brinton's Quarry, Chester 



County, Pa, 



A. Clarke and Schneider;^^ B. Koenig;^' C. 

 roneous analysis by Brush is omitted.^* 



A 



SiOj 34.20 



Al,03 16.58 



Fe^O, 7.41 



FeO 1.13 



MgO 20.41 



H,0 21.14 



100.87 



99.69 



99.47 



22 Am. J. Sci. (3), 40: 452, 1890. 

 23Proc. Am. Phil. Soc, 13: 392, 1873. 



2" Am. J. Sci. (2), 31: 370, 1861. Previous to this the mineral had been known 

 to collectors under the name of phlogopite. 

 2* Taken from Koenig's determination. 



