90 PROCEEDINGS OF THE ACADEMY OF [1890. 



W. 20° S. .4 miles from Glenside, on the east side of the Limekiln 

 Pike, the Potsdam is best exposed. This is in a quarry about a 

 hundred yards south of the Waverly road, but the same belt is con- 

 spicuously exposed on the Waverly road southeast and southwest of 

 the pike, the Waverly road changing its direction from northwest 

 to southwest at the pike and hence crossing the belt twice. The 

 Potsdam here makes a ridge or hill, known as Waverly Heights, 

 southeastward of the Laurentian hill. In the quarry it looks ex- 

 ceedingly like that in the quarries to the northwest (Barren Hill belt) 

 except that the bedding is less regular, the quartz more cherty, and 

 the rock harder. In the quarry the strike was N. 80° E. dip 70° 

 S. E., on the road southeast N. 70° E. dip S. E., and on the road south- 

 west N. 65° E. 70°-80° S. E. Southeast of this no exposures were 

 seen, but there were schistose fragments. The strike of the Potsdam 

 carries it into the bold hill to the northwest, the southeast hill of the 

 Whitemarsh or Montgomery valley, Potsdam entirely at Edge Hill, 

 l)ut further southwest covered with Laurentian fragments and con- 

 tinuing (of schists) to form Chestnut Hill. The soil seems deep, and 

 no exposures were observed. One mass of Bryn Mawr gravel was 

 seen. 



On the Paper Mill road, which skirts the hill on the northwest, 

 :SOuthwest of the road which southeastward forms the northeast line 

 of Philadelphia, the ground is low until within a half mile of the 

 turnpike. Here is a spur of Chestnut Hill, and on the road cutting 

 :at the summit is Laurentian, poorly exposed, consisting of one large 

 mass, and eight smaller, all having exactly the same strike about 

 N. 35° E., and therefore I believe in place. 200-300 feet S. W. is 

 Potsdam abundant, striking N. 80° E. ; following this, are schists in- 

 terbedded apparently with Potsdam ; mostly soft and decomposed 

 but showing the same strike and probably a steep easterly dij). 



These schists resemble very strongly the schists southeast of the 

 Laurentian west of the Schuylkill which include a white rock closely 

 resembling the Potsdam, 



I believe this to be an unconformable contact between the Lau- 

 rentian and the Potsdam and that the schists immediately southeast 

 of the Laurentian are Potsdam. 



It is, of course, possible that these schists are more recent than the 

 Potsdam, and formed from its debris, but the evidence seems very 

 strong that here at least they are not older. 



