1883.] NATURAL SCIENCES OF PHILADELPHIA. 245 



has a more northerly trend in Easttown, is interesting, but not Tieto." 

 My words were : " A mile southeast of Berwyn, the latter can 

 be seen almost, if not quite, in contact with the serpentine, the 

 trap, however, being on the south of the serpentine. The same 

 is true south of Paoli, except that the trap appears to be on the 

 north side." Prof. Rogers (p. IfiS) speaks of this trap as 

 ''occurring along and outside the northern edge of the serpentine, 

 in a succession of narrow, elongated d^'kes, ranging more north- 

 east and southwest than the serpentine. These I have not 

 examined, but such structure agrees precisely with what I have 

 observed of the serpentine further east." 



This interesting occurrence is not upon the map in C 4 ; no 

 trap whatever is shown north of the large serpentine outcrop 

 south of Paoli.' 



Dr. Frnzer {J. Frank. /??.';;., October 1883) kindly compares my 

 criticism with those of the good old gentlemen who, during the 

 war, criticized the army officers, from a safe distance at their 

 comfortable breakfast tables. This is not fair ; every observation 

 I have made has been made on the spot and on foot, and in proof 

 of this Dr. Frazer has not pointed out a single error of fact. Had 

 all the observations in C 6 and C 4 been similarl}^ made, many 

 blunders like those of serpentine in the Bryn Mawr cut, in the 

 cut northwest of Wayne, and on the Gulf road north of Matsons' 

 Ford road, would not have appeared. 



" But it is not a fact that Rogers' altered piimal is a well- 

 defined rock ; pn the contrary, a more heterogeneous collection of 

 gneiss, mica schists, hydro-mica schists, chlorites, feldspar por- 

 phyries, clays, and quartz slates than are found in the regions 

 which he colored as altered primal it would be difficult to collect 

 from the two hemispheres." — Dr. Frazer, J. F. I., October, 1883. 



I referred to the rock described by Rogers. Is it not possible 

 that Dr. Frazer has included, in the above, adjacent rocks which 

 Rogers had no intention of including, as the scale of the map 

 precludes the possibility of accurate ma])ping; and the rocks men- 

 tioned by Dr. Frazer do lie adjacent; but the peculiar rock here 

 shown and so well described by Rogers, is, at least through Lower 

 Merion, Kadnor and Easttown, very well defined indeed. Its 

 breadth nowhere exceeds 800 feet, I think, and this, on Rogers' 



I In my leview, J. F. I., September, 1883, I inadvertently located this in 

 Easttown. It is really in Willistown. 



