647 



Mr. C. E. Hall exhibited specimens from boulders in West 

 Philadelphia, and specimens from outcrops in and behind 

 the Blue (Kittanning) Mountain, to enable the members to 

 compare and identify them. He exhibited, also, a local map 

 on which each boulder was exactly placed and numbered. 

 In the collection was one piece of trap, and several of Trias 

 sandstone. The rest were Oneida conglomerate, and Oris- 

 kany sandstone (conglomerate). Mr. Hall expressed his 

 conviction that most of the Philadelphia gravel was merely 

 disintegrated conglomerate the pebbles of which had been 

 set free in their original rolled state and not re-rolled to 

 any extent. Many pieces were flat and yet in an erect atti- 

 tude, showing ice rather than water transit. The trend of 

 the belt of boulders, so far as studied, was roughly at right 

 angles to the bed of the Schujdkill at tbe Zoological Garden. 

 Mr. Hall had noticed a sort of smoothing oS of the surface 

 of the upturned mica schist country. In some cases the bould- 

 ers were of large size, and grooved as well as polished. One 

 of them contained many Silurian fossils. 



Mr. Price invited Mr. Hall's attention to quantities of 

 boulders being uncovered in the sand cuttings at 25th street 

 and Fairmount avenue, on the eastern side of the Schuyl- 

 kill. 



In the discussion which ensued the possibility of iceberg 

 action and the existence of gravel mounds across the interior 

 valleys were brought into view. 



Prof. Frazer wished to record the fact that he had met 

 with considerable numbers of glaciated (grooved) pieces of 

 Rogers' jasper-rock. Hunt's orthophyre, or as he preferred to 

 call it, felsite porphyry rock of the South Mountain, along 

 the low pass (partly a gorge) through which the Gettysburg- 

 Chambersburg road leads. He suggested, for a cause, a thin 

 glacier coming across from the Path Valley, west of Cham- 

 bersburg. 



Mr. Lesley described Mr. John Harger's (of Oxford, Conn.) 

 method of obviating parallax in reading the vernier on the 

 dial plate of a transit instrument or surveyor's compass ; viz. 



