1890.] NATURAL SCIENCES OF PHILADELPHIA. 105 



Prof. Rogers, whose plutonic views as to most of the serpentines 

 are well known, recognized this belt to be an altered schist though 

 he regarded it as " metamorphosed by infusion of magnesian matter 

 from the dyke of intrusive serpentine which everywhere adjoins it."^ 

 But it is this " intrusive serpentine " which contains the pseudomorphs 

 after staurolite. 



This belt has afforded more minerals than any other serpentine 

 of the region, except, probably, Wood's mine in Lancaster county, 

 perhaps because of the more extensive quarrying in it. Dolomite is 

 abundant, sometimes in peculiar crystallizations. The following also 

 have been found, Breunnerite in fine crystals, chalcopyrite, bornite, 

 magnetite, tremolite, staurolite, actinolite, chalcanthite, epsomite, 

 Millerite, apatite and Hallite. Southwestward of the Schuylkill it 

 appears at numerous outcrops ending on the Black Rock road about 

 a mile northeast of Bryn Mawr. 



The Cresheim Creek Outcrop, and Small 

 Outcrops near Media. 



Near the mouth of Cresheim creek on the Wissahickon in Fair- 

 mount Park, Philadelphia, are two small outcrops of actinolite and 

 antholite. The southeastei'ly, about 700 feet S. E. of the mouth of 

 Cresheim creek, is well known. It lies about two miles south- 

 east of the steatite belt, and is wholly within the schists. Mr. Hall 

 mentions a similar outcrop at the Flushing school-house in Bucks 

 county, and excepts these from his generalizations as to the serpen- 

 tines. The outcrop is immediately in the Manayunk schists, is quite 

 insignificant and appears to be a local alteration of hornblende-like 

 rock. About 500 feet N. W. of Cresheim creek is another similar out- 

 crop much better exposed, which, I believe, has never been described. 

 It appears undoubtedly interstratified in the schists with a dip of 

 about 45° N. 40° W. The schists can be seen almost in contact 

 (within one foot) and the dip and strike of the antholite and of the 

 schists seem the same. The schists contain garnets and staurolite. It 

 is with these I should class all or nearly all the outcrops southwest 

 of the Marple Barren Hill school-house and also those southwest of' 

 Media, including a part if not the whole of the great outcrop west, 

 of INIedia. 



In Mr. Hall's map of Delaware county published in C^ are 

 shown a number of outcrops of serpentine extending southwestward 

 1 Geol. of Pa., Vol. 1, p. 71. 



