116 PROCEEDINGS OF THE ACADEMY OF [1890. 



of the Manayunk group. A recent careful examination confirms me 

 in this and indicates that the serpentines of this vicinity, like those 

 farther east, are altered beds in the Manayunk gneisses. 



The serpentines are shown on Mr. Hall's map as four distinct out- 

 crops, one on each side of the creek, on a line passing N. 50° E. 

 through Glen Mills, and two on a parallel line about three-quarters 

 of a mile S. E. near Sharpless' feldspar quarry. 



The outcrop west of the creek nearest Glen Mills is confined to a 

 very trivial exposure in the road. That southwest of it I could not 

 find. East of the creek were trivial exposures of honey-comb quartz 

 loose on the surface, but I believe considerably north of Mr. Hall's 

 line. 



At Glen Mills, the topographical base of Mr. Hall's map is incor- 

 rect or the roads and railroad have been changed since it was made. 

 The road to Sharpless' quarry is correct and the green spot at its 

 westerly termination correctly indicates the location of the serpen- 

 tine there. The railroad north of this crosses the old creek bed as 

 shown, diverting the creek to the west side of the railroad, which, 

 however, does not continue on the east side, but crosses immediately 

 below Glen Mills station, and thence continues on the west side. 

 This crossing and the station are about a half mile north of the road 

 to Sharpless' quarry, and at this point there is another bridge over 

 the creek connecting four converging roads, or more accurately, per- 

 mitting the road along the creek to cross, going northwardly, from 

 the w^est bank to the east, and a northeast and southwest road to 

 cross the creek. It is on this last road I observed the honey-comb 

 quartz east of the creek. On Mr. Hall's map these roads are 

 located a considerable distance north of their true position. 



Beginning at the creek about a half mile north of Glen Mills sta- 

 tion and this bridge, at the point at which on Mr. Hall's map, trap 

 in Laurentian is indicated, a very compact garnetiferous gneiss is 

 found. South of this, a recent cut for a railroad to the n^w House 

 of Refuge shows the same gneiss interbedded in the Manayunk 

 gneisses, some decomposed, some not, some contorted, some regular, 

 showing a strike about N. 20° E. with a southeasterly dip of 20° to 

 50°. South of this is another excellent exposure on the railroad and 

 about here should'be the northerly margin of the schist area, but the 

 same rocks appear, and continue with constant exposures, down the 

 creek to and beyond the Sharpless road. Close to the road and to 

 the north of it is a quarry evidently not wrought for many years. 



