180 PROCEEDINGS OF THE ACADEMY OF [1892. 



hornblende gneiss of the lower part of the quarry seemed to decom- 

 pose into the philadelphite schist near the surfiice, I think the 

 philadelphite is due to the alteration of hornblende. 



Except sphene and bornite I know of no other mineral found 

 here. About a quarter of a mile further west in a road-cutting were 

 large quantities of a feldspar, probably orthoclase containing im- 

 perfect crystals of a black mica, probably lepidomelane, frequently 

 five or six inches in length and not over an inch across. Further 

 west and close to the Wissahickon is the well known McKinney's 

 quarry to which the attention of mineralogists was first called by 

 the abundance of apatite. The gneiss here is very regular and of 

 excellent quality. In a bed of feldspar met with about 1850 

 rough irregular crystals of apatite, some a foot long, were found 

 abundantly. Besides this the following were found ; natrolite, heul- 

 andite, laumontite, hornblende, bornite, chalcopyrite, malachite, 

 chrysocolla, fahlunite, sphene and a micaceous mineral resembling 

 philadelphite. Some of the laumontite was colored green by 

 copper. 



Northwest of the Philadelphia mica schists and gneisses, from the 

 Schuylkill to near Morton Station, southeast of Media, extends an 

 outcrop of porphyritic gneiss which appears to include some small 

 schist areas, and this is followed by schists called by Mr. Hall the 

 Manayunk schists, very similar to those on the southeast of the 

 porphyry. Both the porphyry and the schists are very barren of 

 minerals. The porphyry is, of course, full of feldspar (orthoclase) 

 crystals usually if not invariably twinned, but it is impossible to 

 detach them from the gangue, and nothing but sections can be had. 

 In the porphyry, granitic segregations occur, comj^osed chiefly of 

 a reddish orthoclase making sometimes a graphic granite. Quartz 

 is much less in quantity than the orthoclase, and mica (muscovite) 

 even less than the quartz. Rarely in this granite occurs black 

 tourmaline in poor specimens. Near West Laurel Hill Cemetery 

 minute sphenes occur in the gneiss which is there very fine grainecl. 

 Northwest of the bridge of the Reading Railroad over the Schuyl- 

 kill at the Falls was formerly a large quarry in a gneiss resembling 

 the Fairmount gneiss, but harder. 



On the west bank of the Schuylkill, just above the Park bridge, 

 is a quarry which at one time was lai'gely wrought. The rock is 

 not distinctly porphyritic, and is very variable in its different strata, 

 passing from a highly felspathic gneiss to a mica schist, and from 



