1892.] NATURAL SCIKNCE8 OF PHILADELPHIA. 175 



spar has become kaolin and the mica, in some cases, a vermicnlite. 

 Mill Creek flows into the Schuylkill River about three hundred 

 yards above Gray's Ferry, and on its banks some quarrying has 

 been done in the mica schist, but no minerals were found except 

 apatite and albite in poor specimens. In the sand of the Schuylkill 

 above Gray's Ferry, and probably elsewhere, small zircons occur. 



On mica schist rocks near Gray's Ferry, exposed in a cut of the 

 Philadelphia, Wilmington and Baltimore R. R., an efflorescence 

 proved to be glauberite but it is possible that this may have been 

 derived from the gunpowder used in blasting. 



The mica schists continue about two miles up stream to Fair- 

 mount, whose bold hill, is composed of a gneiss which appai'ently 

 rises as an anticlinal through the schists and is exposed by erosion 

 On the western side of the river this rock was largely quarried. 

 The first quarry opened was immediately on the river bank. When 

 the inclined plane was abandoned the Pennsylvania Railroad made 

 a curved cut throu2:h these rocks extending from about 30th Street 

 to 34th Street, and a large quarry, or a series of quarries afterwards 

 merged into one, was opened on the southwest side of the railroad. 

 Subsequently the bluff" between the railroad and the river was 

 largely quarried away, leaving an almost vertical wall of some fifty 

 feet in height. This gneiss, identical with that found on Ridley and 

 Crura Creeks in Delaware County, contained segregated masses of 

 coarse orthoclase-albite-muscovite-granite. In this granite most of 

 the minerals were found. Those identified are as follows : 



Orthoclase in fine crystals, nearly all obtained from one highly 

 quartzose granite bed near the river. 



Albite, found with the orthoclase, but usually somewhat decom- 

 posed, and sometimes wholly converted into kaolin, the orthoclase 

 remaining unchanged. 



Tourmaline, black, in good crystals, sometimes terminated and 

 sometimes large, but usually very brittle, so that good specimens 

 were difficult to procure. 



Beryl, rare and in small crystals, sometimes much decomposed. 



Autunnite occurred in crystals and also as crystalline coatings 

 loosely implanted on the rock. It was at times quite abundant and 

 in very fine specimens. It was not usually in the granite but 

 chiefly occurred in seams in the gneiss. 



Chalcolite, perhaps a half dozen specimens wei-e found associated 

 with the autunnite. 



