1890.] NATURAL SCIENCES OF PHILADELPHIA. 113 



and forming slabs. The numerous joints in the rock cause many of 

 these to break up into i)ieces too small for use, and the quarry 

 has not been wrought for some time. The whole quarry is in 

 serpentine, but the north wall is granulite. At the contact there 

 is a stratum about one foot thick of soft micaceous rock like Hallite 

 or JefFerisite. In the granulite are lenticular masses of the Hallite. 

 Farther southeast is a section of this granulite, and there appears on 

 the northwest, serpentine, then a thin stratum of Hallite, then 

 granulite fragmentary, then a V-shaped mass of Hallite and frag- 

 mentary granulite, then serpentine. The strike is about N. 50° E. 

 and the dip curves 70° southeast on the southeast side, to 80° north- 

 west on the northwest side. Some of the granulite resembles the Lee- 

 lite of southern Chester county which passes into Deweylite. This 

 •exposure is 10 or 12 feet across and the appearance is that of a dyke. 

 About fifty feet southeast of this is a similar exposure, of similar 

 character, with strike about the same, dip 70° southeast, and on the 

 northwest of it, Hallite enclosing decomposed granulite. 



The ravine northwest of this shows few exposures, but granulite 

 is abundant, here inclosing sunstone and Amazon stone. 



South of the Black Horse Inn is one of the largest areas of 

 serpentine, and in this, a large quarry w'as wrought for many 

 years. In this vicinity large masses of granulite are abundant, some 

 of them containing very beautiful moonstone. Here occurs also 

 corundum in crystals in albite, the locality being about a quarter of a 

 mile south of the Black Horse Inn on the road to Elwyn. On this 

 road the chief rock is the schists, with serpentine close to the Inn, 

 and also about a quarter of a mile north of the railroad, the latter 

 apparently not over 50 feet wide. 



For brevity, I have used the term granulite to indicate the feld- 

 spathic rock so abundant in this region. Most of it is strictly gran- 

 ulite, a mixture of feldspar and quartz, the feldspar fi'equently oligo- 

 clase and gi-eatly predominating, some of it probably containing no 

 quartz at all. In some of it hornblende occurs but usually in very 

 small proportion, as in the so-called granite quarries on Chrome 

 Run near the State road. In the schistose varieties mica occurs, but 

 it is probably absent in the compact varieties. Some of it is very 

 fine grained, some coarse with crystals of feldspar an inch or more 

 across, in fact a porphyry. In decomposing some of it bi-eaks up 

 into small angular fragments, which are quite hard, and some of it 



