302 PROCEEDINGS OF THE ACADEMY OF 



plane, but in tlie others, when notjointed, irregular and sometimes 

 conchoidal. 



At a quarry on the northern edge of this gneiss, north of Frank- 

 ford, Apophyllite was found; its only place of occurrence in the 

 neighborhood. 



At the line between Philadelphia and Montgomery counties, 

 the well-known steatite bed, beginning on the west side of Chest- 

 nut Hill, about three miles distant, crosses the Schuylkill and 

 coiitinues in a nearly southwest by south direction (exactly S. 

 54 W.), bej^ond that river about two miles and a half, where it 

 crosses the valley of Mill Creek, and ends, or sinks beneath the 

 surface. Perhaps the most conspicuous and remarkable rock of 

 this belt is a steatite, containing a l)lack serpentine. This rock 

 in man}' places projects above the surface of the ground in im- 

 mense masses, particularly at Mill Creek, seeming to have re- 

 sisted erosion and decomposition to a remarkable degree. It lies 

 on the northwest side of the steatite proper. The whole aspect 

 of this curious formation suggests a rock originally containing 

 crystals of some mineral, but metamorphosed almost beyond 

 recognition. To this mineral I believe no clue has heretofore 

 been obtained. Isearly all these black masses, which vary in size 

 from a half inch or less to several inches, are irregular in form, 

 and adhere so closely to the matrix that sections onl}^ can be ob- 

 tained, which, however, rarely show any angles or other than a 

 nodular form, so that the rock has by some been considered a 

 conglomerate. Even in weathering, the two, except in one place 

 hereafter mentioned, seem to weather so much alike that no clue 

 to the form can thus be had. 



About two years ago, however, I found near the soapstone 

 quarry, on the northeast bank of the Schuylkill, one of these ser- 

 pentine masses presenting a stellated form of six ra3^s, or of one 

 large cr3'stal crossed b}^ two smaller at angles of about GO and 

 120 on the section plane, suggesting staurolite. A few days ago, 

 while with Prof. E. J. Houston examining this rock on the south- 

 west side of Mill Creek, a piece was found containing a broken 

 crystal 4i inches x 1^ X 1^, presenting two well-defined sides, 

 and upon a cross-fracture, these sides were found to continue to 

 another formino- with one of the sides an angle of about "75° on 

 the section, which approximated a plane at right angles to the 



[February 13, 



