50 EDWIN W. HUMPHREYS AND ALEXIS A. J V LIEN 



Glacial deposits. — The layer of glacial deposits, which overlies 

 the schist at this locality, as shown in the following generalized 

 cross-section along Westchester Avenue (Fig. 4), about fifteen feet 

 from the street level to the greatest depth in the excavation, is yet 

 to be considered. 



Feet 



Fawn-colored micaceous sand with some trap bowlders .... 3-5 



Slab of pegmatitic gneiss 1 



Gray sandy till, with striated bowlders \ 



Slab of pegmatitic gneiss 1 



Gray till, rich in micaceous clay \-h 



Slab of pegmatitic gneiss \-h 



Gray bowlder clay §-3 



Slab of pegmatitic gneiss J-22 



Blue-gray bowlder clay f 



Slabs of pegmatitic gneiss and Manhattan schist i\ 



Blue-gray bowlder clay 1 



Decayed schist in place with vertical foliation, intercalated 

 with thin seams of pegmatite 6—82 



The remarkable deposit of ground moraine, which here rests 

 upon the upturned edges of the schist, is thus found to consist 

 largely, in the two hundred feet of section exposed along the two 

 avenues, of a succession of huge, overlapping sheets of granitic 

 gneiss separated by layers of sand and till or bowlder clay. 



The gneiss slabs, of which a series of from four to eight are 

 shown in any particular part of the section, consist of a rather 

 fine-grained granitoid gneiss of constitution similar to that of the 

 pegmatite. Their dimensions in cross-section vary from about 3 

 to 35 feet in length, and in thickness from 1 to 30 inches or more. 

 There was no opportunity to determine their real shape, but appar- 

 ently they consisted of flat sheets, often thinning down toward the 

 edges to an inch or less. Some show fracture and faulting in place, 

 as by the effect of superincumbent pressure (Fig. 5), and occasion- 

 ally the extension of such a slab toward its edge into a thin pliable 

 sheet, one or two inches thick, reveals a marked curvature as by 

 pressure from above (Fig. 6). Toward the bottom of the section, 

 they may be accompanied by a few small sheets of fine biotitic 

 schist, like that of the underlying rock in place. The granitoid 

 gneiss in these slabs shows partial to thorough decay, so that they 



