242 PROCEEDINGS OF THE ACADEMY OF [1883. 



speaks of finding sandy gneiss^ with a hard serpentine-like mineral. 

 I have also the enrite of Barren Hill for comparison. 



It will be seen that the correspondence is exact — the micaceous 

 partings, the rhomboidal cleavage, the minute tourmalines — all 

 agree. 



I have also a specimen of the trap of the Conshohocken dj^ke 



whicli crosses this cut about 100 feet southeast of the eurite. I 



'could find no serpentine-like rock there, nor any other hard rock; 



the rocks are^much decomposed, but the gneiss of Rogers' altered 



primal is there unmistakabl}'. 



2. I have also specimens (loose in the soil) from immediately 

 south of the eastern end of the serpentine, stated, on p. 87, to be 

 bounded both south and north bj- talcose slate. The rock is 

 Rogers' altered primal. 



3. On page 87 it is stated : " It is evident that even a synclinal 

 belt of serpentine 2000 feet wide, or even 400 feet wide, can mean 

 nothing else than a great thickness of the talc mica schist forma- 

 tion, metamorphosed more or less completely into serpentine, and 

 a good cause for such alteration is present in an extensive out- 

 burst of trap close beyond." 



" Everybody familiar with the surface of Delaware and Chester 

 counties knows how almost invariably its trap and serpentine 

 appear together." 



If this is true, how can it be explained that a few miles further 

 east, what seems to be admitted (p. 282 to be the same serpentine 

 belt is wholly within the gneisses of C 6 (Rogers' altered primal), 

 over 1000 feet south of the trap, with gneiss, hornblende schist, 

 steatite and limestone intervening, and that the trap passes east- 

 ward for some five or six miles, at least, from Wayne station, 

 P. R. R., to a point far east of Conshohocken, through the hydro- 

 mica schists of the South Valley Hill to Bethel Hill without a 

 trace of serpentine. 



At what locality in Delaware county, among its numerous ser- 

 pentine outcrops, does trap, properly so-called, occur? 



It does not appear at Lenni, Media, Blue Hill, Marple, New- 

 town, nor at any of the numerous outcrops of the Lafa3^ette belt, 

 nor of that of the steatite belt on the south, nor of the Radnor 

 belt in Radnor. In Easttown they do appear together, but can 



' This quotation is erroneous ; in place of "sandy gneiss" it should be 

 "a decomposed friable white gneissoid rock." 



