394 JULIEN 



quarry, and more recently by the United States Geological 

 Survey, in note of its location on the sheet for New York City/ 

 Between the last northward turn of that creek and the Hudson 

 river, the extreme northern end of Manhattan Island projects, 

 for a distance of about one quarter of a mile, as a forest-covered 

 rocky promontory, reaching a height of nearly 225 feet above 

 the sea-level. 



The following appears to be the succession of beds. The 

 lowest, foliated micaceous gneiss, often slaty in structure, envel-' 

 oping the sheet of hornblendic rock. Above this, a similar 

 gneiss, with many garnetiferous layers, six to nine decimeters 

 in thickness, much gnarled and contorted. The enclosed 

 roughly crystallized iron-garnets vary from one to three centi- 

 meters in diameter. Some layers are white, fibrous and thinly 

 laminated, rich in parallel flakes of a quartz-fibrolite mixture. 

 The highest beds, forming the crest, consist of alternations of 

 micaceous gneiss with layers rendered granitoid by saturation 

 with pegmatite in seams and lenses, often presenting an augen- 

 structure. 



Along a slope of 30° which forms the steeper eastern side of 

 the promontory, a belt of hornblendic rock extends continuously, 

 a little above the shore, from a point near 214th Street, for a 

 distance of more than 1,000 feet, until it passes beneath the 

 creek at the northern end of the outcrop. It is intercalated in 

 the bed of foliated micaceous gneiss with generally coincident 

 strike. This gneiss overtops it on the west, forming the sum- 

 mit of the ridge, and also underlies it on the east, along the 

 shore of the creek. There is much fallen talus, but the contact 

 of the hornblende-rock with the gneiss on either side is un- 

 covered in several places, sometimes with so sharp a line of 

 demarcation that one may set one's foot on both rocks at their 

 junction. No difference was distinguished in texture or consti- 

 tution of either rock near the line of contact. The thickness of 

 the dioritic sheet was estimated at about 35 feet for a large part 

 of its course. The bed of the creek is known to be occupied 

 by crystalline limestone, and a little valley on the east of the 



' Geol. Atlas of U. S., N. Y. City Folio, No. 83, Washington, 1903. 



