-Nov. 5, 1875.] ^^^ [Hall. 



ON GLxlCIA-L DEPOSITS AT WEST PHILADELPHIA. 



(with a map.) 



By Charles E. Hall. 



(Bead before the American PMlosopliical Society, November 5, 1875.) 



In a preceding paper on Glacial Deposits in Carbon, Northampton, and 

 Monroe Counties, published in the Proceadiugs of the Philosophical So- 

 ciety, I proved that the glaciers passed through the gaps of the Kitta- 

 tinny Mountain and followed somewhat the courses of the present river 

 beds, at all events toward the close of their existence. 



The southern boundary of the Glaciers is a question which will require 

 much careful study to determine. It is, however, probable that they 

 reached much further south than generally supposed, and it would scarce- 

 ly be probable that a mass of ice, great enough to pass over the highest 

 ranges of the White, Green, and Adirondack Mountains, to suddenly end 

 at so short a distance as the Blue, or Kittatinny Mountain. 



I will take this opportunity to speak of the double systems of Glacial 

 scratches so plainly marked in the more northern country. I have ob- 

 served on the shores of Lake Champlain, the polished surfaces indicating 

 a movement of the ice in a line nearly parallel to the lake, or a south- 

 erly movement, while a few miles back from the lake, many of the 

 valleys are crossed by moraines, which indicate Glaciers moving in an 

 easterly and south-easterly direction towards the lake, and polished 

 surfaces and scratches indicating the same. I concluded from this that 

 one system of scratches indicate the course of the moving ice when it 

 was so great as not to be influenced by the topographical features of the 

 country. And the second system, formed after the mass had so melted 

 away that it followed the depressions of the surface. 



It is my object, in the following, to show that we have Glacial deposits 

 within the limits of the City of Philadelphia. Since my residence in this 

 City the alluvial deposit has occupied my attention. It is composed of 

 sand, rounded quartz pebbles, and gravel, of sandstone and conglomerate. 

 It varies in depth from two and three feet to twenty-five. Intermingled 

 with the rounded quartz pebbles, are found everywhere, angular pieces 

 of softer sandstone, as Medina and New Red, which would necessarily 

 have been worn into rounded pebbles and sand had they been associated 

 with the quartz when it was being foi-med into pebbles. The conclusion 

 I therefore come to is this, that the quartz pebbles of this region, perhaps 

 also, of the Atlantic coast, is the debris from the decomposition and disin- 

 tegration of the older rocks as the Oneida conglomerate, coal conglomer- 

 ate, etc., and brought here principally by the ice and water of 

 Glacial time. About the first of October, I made the first critical 

 examination of the land lying between Spruce and Walnut streets 

 and west of Forty-fifth street, where the sand and gravel has bsen ex- 

 cavated to, or within a short distance of the bed-rock. Here are exposed 



