'i^O PKOCEEDINGS OF THE ACADEMY OF [1894. 



Christiana it contains garnets, at Brubaker's magnetite, and at Hoof- 

 raau's altered pyrite. At Hoofman's, in small quantity, is a crypto- 

 crystalline variety, very soft, very pale green, nearly white in color, 

 and resembling the talc schist of Lafayette. At the Swan outcrop 

 chlorite in large folia occurs, also a rock apparently one of the 

 hornblende family changing into steatite or chlorite. 



At the Windle outcrop the masses of steatite so closely resemble 

 the adjacent masses of schistose gneiss that one is in doubt until he 

 tests for hardness, and there appears to be a gradation from the very 

 hard to the very soft rock. 



I have stated that these outcrops are in the Chester County 

 gneiss, but to this the William Paxson outcrop may be an exception. 

 There is an outcrop of the ancient gneiss to the southwest of it. 

 The exposures do not suffice to indicate much more than its certain 

 existence. 



There is one other outcrop of steatite to which my attention was 

 called by Mr. Windle, further north than any of those already 

 mentioned and apparently isolated. It is on the farm of Samuel 

 Holmes, and on the south branch of Birch Run, an affluent of the 

 west branch of the Brandywine, in West Cain Township, Chester 

 Co. , and is in the course of the ancient gneiss, which ranges north of 

 the sandstone, north of the Chester County gneiss, in West Cain. As 

 usual the exposure is poor, consisting of but a few loose masses of 

 steatite, with masses of schistose gneiss resembling it in appearance. 



Perhaps the most striking feature at all these outcrops, considered 

 in relation to those on the southerly side of the valley is the rarity 

 of serpentine. At all other steatite outcrops in S. E. Pennsylvania 

 of which I have knowledge serpentine rocks abound, and the steatite 

 rocks are subordinate, except perhaps in the Lafayette steatite belt, 

 but in it serpentine is abundant though the steatite predominates. 

 In these outcrops north of the valley, however, serpentine is quite 

 rare, hemg found at the Swan outcrop only. The resemblance of 

 the steatite to the gneiss found with it is very similar to the occur- 

 rence at Chestnut Hill, north of Easton, Pa.,® and my observations 

 lead me to the conclusion that the genesis is the same in both in- 

 stances, the alteration of a gneiss containing probably a large pro- 

 portion of a magnesian mica, and this perhaps derived from the 

 hornblende, as is certainly the case on the Schuylkill, above Girard 

 Avenue Bridge, Fairraount Park, Philadelphia. 

 * Proc. A. N. S. Phila., Mar. 25, 1890, p. 95. 



