456 PKOCEEDINGS OF THE ACADEMY OF [1894. 



On the contrary, the rock next north of the Cambrian sandstone is 

 sometimes schistose, and while often gnesssic, is not nearly so densely 

 crystalline. The quartz is usually colorless or white. The rock 

 varies greatly, though the quartz — ^orthoolase variety, of coarse tex- 

 ture, is most abundant. AVhile, as a whole, differing from any other 

 gneiss of southeastern Pennsylvania, it is more unlike the ancient 

 gneiss than it is unlike those southeast of the Trenton — North Brook 

 ridge, that is the gneisses of Rogers' first belt, Mr. Hall's Phila- 

 delphia and Manayunk schists and gneisses. To the last, as a whole, 

 the resemblance is not close, but the I'ock of some strata in each bear 

 a resemblance. It is the rock referred to by Dr. Frazer as " a rock 

 of doubtful signification called alternately conglomerate, feldspar 

 porphyry, etc." (C^ p. 221.) Although Dr. Frazer in his text 

 differentiates this rock,* on the map, it as well as the schists between 

 the Cambrian and the limestone are colored the same as the ancient 

 gneiss, though Dr. Frazer queftions whether it is not really lower 

 Cambrian.^ 



At Valley Forge and eastward there is in the same relation to 

 the Cambrian sandstone a coarse conglomerate of pebbles chiefly of 

 bluish and pinkish quartz, which has been referred with little doubt 

 to the lower Cambrian. Could we be sure that this quartz feldspar 

 rock represents the conglomerate, a point would be gained, but inas- 

 much as they are extremely unlike, although exposed within five or 

 six miles of each other, I think we need proof of their identity. The 

 best exposure is along the west branch of the Braudywine, north 

 of Coatesville, where they dip quite irregularly, but with a prevailing 

 southeast dip of 70° and upwards. 



As this rock resembles closely no other southeast of the red sand- 

 stone, and occurs, so far as I am aware, only in Chester County 

 and the adjoining county of Lancaster, I propose for it provisionally 

 the name of the Chester County gneiss. 



It is in this gneiss that most, if not all, of the outcrops of the 

 Sadsbury steatite occur, and apparently in two lines somewhat 

 irregular. 



The easternmost outcrop of the northerly line is on the farm of 

 Mr. Thomas H. Windle,^ on the left bank of the West Branch of 



» Second Geol. Surv. Peuna., vol. C, pp. 221, 225, 228, 257, 263. 



'•^ C*, pp. 257, 258. 



^ I am under obligations to Mr. Windle for aid in this investigation. 



