1890.] NATURAL SCIENCES OF PHILADELPHIA. 85 



some of the Chestnut Hill rocks, occur between outcrops of the 

 porphyritic gneiss, all dips seeming to be northerly. Among the 

 schists there are outcrops of a granite differing from that of the 

 Fairmount gneiss as before described. 



Examining the section exposed along Darby creek, we find mica 

 schists and gneisses of the Manayunk varieties, both feldspathic and 

 hornblendic ; indeed some of the hornblendic variety is almost en- 

 tirely hornblende with a little quartz, or a diorite. The porphyritic 

 gneiss occurs, and not far from it the soft mica schists, here in many 

 of the beds, little more than granular quartz with a little mica form- 

 ing whetstone, but in these occur beds of hard granitoid gneiss and 

 of hornblendic gneiss. 



Along Crum creek we find at Avondale an outcrop of the Fair- 

 mount gneiss well exposed by quarries, it being the most valuable 

 building stone of this part of the State and at this point and on Rid- 

 ley creek can be well seen the segregated masses of coarse granite 

 which have here, as well as at Fairmount, yielded to mineralogists 

 fine cabinet specimens of interesting minerals most of which are 

 confined to this stratum. 



• Above this, near Swarthmore, is a considerable exposure of mica- 

 ceous gneiss and mica schist, some of it very compact and hard and 

 some of it containing garnet and audalusite. In this neighborhood 

 occur also hornblendic schist and gneiss in considerable quantity. 

 Northwest of this is the most westerly outcrop of the porphyritic 

 gneiss of which the writer is aware. It is on the road leading north 

 from Morton station one hundred yards north of the turnpike and 

 about a mile from Morton. The strike is N. 10° W. dip 75° N. E. 

 North of this are decomposed schists, with no good exposures. The 

 strike near Trout Run was N. 10° E., the dip 30° to 60° S. E., 

 and the schists were apparently of the Chestnut Hill group. Here, 

 interbedded in the schists, are narrow beds of a syenitic gneiss which 

 seems to be characteristic of this horizon. Rarely seen in place, it 

 is found southeast of the Laurentian from the Schuylkill to Crum 

 Creek strewn over the fields and along the roads, conspicuous by 

 reason of the hornblende in it being very evident on the exposed 

 surfaces as small crystalline masses, and by its invariably undecom- 

 posed condition. It occurs also northwest of the Laurentian in 

 schists on the property of the late Moro Phillips, about half a mile 

 from the Schuylkill on the southeastern side of Cream valley near 

 Conshohocken. I have observed this rock in place in three locali- 



