86 PROCEEDINGS OF THE ACADEMY OF [1890. 



ties only, that on Trout Run, on the Roberts road at the crossing of 

 the old Lancaster road, and at Moro Phillips'. In none of these 

 were the outcrops over two or three inches wide. 



On Crum creek the porphyritic gneiss has not been observed nor 

 the Chestnut Hill schists, though the latter may be under cover 

 northwest of Palmer Mills. The visible rocks seem all to be of the 

 Manayunk group. 



Along Ridley creek the Fairmount gneisses are exposed and have 

 been largely quarried. On the right bank near the road from 

 Philadelphia to Chester there is a large quarry in hornblendic 

 gneiss directly opposite (about one-eighth of a mile west of) two of 

 the largest quarries in Fairmount gneiss. Above this are schists 

 and gneisses similar to those along Crum Creek, except that north 

 of Media, and also northwest of Media, enstatite appears in the 

 schists. The softer Chestnut Hill schists with their garnets and 

 ragged fracture are not to be recognized. It appears probable that 

 they narrow in INIarple township so as to occupy but two or three 

 hundred feet, between the enstatite-serpentine near the Marple 

 Barren Hill school house, and the antholite-serpentine to the south- 

 east and that they then disappear. The exjiosures however are poor, 

 and this is not certain. 



Along Chester Creek, similar Manayunk schists and gneisses 

 occur, but more massive, and harder, containing more feldspar, 

 hornblende and quartz and less mica. From Bridgewater Station 

 northward, hornblendic gneiss increases in quantity and the felds- 

 pathic gneisses become harder and more massive, but everywhere 

 they are more or less schistose and distinctly stratified, and do not 

 at all resemble the Laurentian of the Radnor-West Chester belt, 

 which, with all its distinctive characters, is found within two miles of 

 them east of Glen Mills. 



Occasional hand sj^ecimens resemble some of the Laurentian, but 

 in the field the differences are striking. 



On the high ground adjacent to all these creeks the decomposition 

 of the rocks has been so great that in comparatively few places can 

 outcrops be observed. The mica schists and softer gneisses become 

 a micaceous and kaolin-like earth. The hornblendic and harder 

 feldspathic gneisses break up into schist-like pieces and these again, 

 when containing much hornblende, into a very deep reddish-yellow 

 soil, in which at moderate depths hornblendic fragments may be 

 found. 



