102 TROCEEDINGS OF THE ACADEMY OF [1890. 



Southwest of this, the next exposure of the serpentine which 

 I have seen is at Blue Hill between Crum and Ridley creeks. 

 This outcrop lies near Sycamore or Bishop's Mills on Ridley creek 

 and nearly in the strike of the LaFayette belt. The Marple outcrop 

 lies south of this line, probably indicating a curve in the Laui'entian, 

 but the adjacent rocks on the northwest are not visible in place at 

 Marple. The elevation of the region immediately northwest is in- 

 dicative of the Laurentian. At Blue Hill the Laurentian again 

 seems to almost surround the serpentine. Just north of the school- 

 house the Laurentian appears in place with a strike nearly south, 

 immediately west of abundant fragments of honeycomb quartz per- 

 haps indicative of underlying serpentine, and not over 300 feet north- 

 west of abundant serpentine in place. Further northeast the Lau- 

 rentian occupies the entire hill, which here is quite elevated, with 

 steep slopes on the northwest and southeast, and a more gentle one 

 on the northeast to Crum creek. 



In the serpentine where it has been quarried on the Providence 

 road opposite the Blue Hill school-house is a small quantity of gran- 

 ulite appai'ently a dyke. On the road along the creek south of the 

 serpentine a decomposed granite or granulite appears, the indications 

 being quantities of small masses of crystalline feldspar. 



The locality southwest of Newtown Square is not well exposed. 

 Laurentian, unaltered, may be seen at the fork of the roads three- 

 quarters of a mile west of Newtown Square and its strike would 

 bring it northwest of, but very close to, the serpentine. The Castle 

 Rock enstatite seems to be continuous with this serpentine, separated 

 from it only by Crum creek and the immediately adjacent low 

 ground. This locality is not far from the Willistown exposure next 

 described and is probably identical with it. 



The Willistown outcrop, like that northeast of Radnor station, 

 appears to be largely within the Laurentian, which extends from 

 West Chester eastward as close to it as any rock can be observed. 

 To the northward Laurentian is everywhere. Following the serpen- 

 tine table land eastward, the serpentine fragments in the soil sud- 

 denly, within less than 100 feet, are replaced b}^ hornblende frag- 

 ments and, a short distance beyond, Laurentian rocks form a steep 

 bluff. This bluff' rises precipitously from the north branch of Ridley 

 creek on the east, and from the Philadelphia and West Chester road 

 on the north. The Laurentian dips S. 25° E. 65°. The rocks are 

 partially exposed along the road and going west are as follows: 



