18 ROCK FLOOR OF GREATER NEW YORK. [bull. 270. 
An excellent example still remains open to examination on the west side of 
St. Nicholas avenue, about West One hundred and thirty-eighth street. * * * 
One such fault vein, 2 feet wide, is rilled by a friction breccia made up of angular 
fragments of the rock inclosed in brownish-white quartz (fig. 1), the walls of the 
fracture lined by hackly projections of the torn rock along both sides, as if they had 
been wrenched apart and rubbed together. 
At other localities, as, for example, at the huge pit on Spuyten Duyvil Creek, por- 
tions of the hornblendic rock are traversed by innumerable veinlets of quart? or 
pegmatite, indicating a shattered and even brecciated mass. 
Julien shows that the hydrated rock masses are in all probability 
altered basic igneous intrusions, the theory of alteration from impure 
Limestones and thai of metamorphism of ferruginous sediments being 
fully stated and rejected. Concerning the stages of metamorphism of 
the district, he says (pp. liM 425): 
The first was concerned in the early consolidation of the sediments, followed pro- 
gressively by their crystalline alteration, with development of certain new minerals— 
biotite, albite, and staurolite. 
Then ensued the general impregnation of all the layers with pegmatitic material. 
\"e\i came the intrusion of a series of pegmatite dikes, cutting each other in suc- 
cession, and all, so far a- yet known, intersecting the pegmatite lenses of the preceding 
generation. With these orogenic movements seem to have been connected, with 
extensive folding, crumpling, ami faulting of all the beds of gneiss, schist, and lime- 
stone, and a further increase of crystalline structure,. development from micas and 
feldspars of another group of minerals requiring a condition of high temperature, 
such as muscovite, sillimanite, fibrolite, cyanite, and tourmaline. 
Finally, down to the present period, ensued the oxidization, hydration, and par- 
tial leeching of the less considerable constituents of the schist by meteoric waters, 
with partial decomposition, etc. 
In regard to the mode of occurrence of the amphibole-sehists, this 
author says: 
These occur interpolated among all the gneisses of the island, and though often 
found in proximity to the limestone are never inclosed by it nor in contact with it. 
He further says: 
These schists have been observed only in the northern part of the island, the 
greater part of whose surface, shown on the map, is occupied by buried gneisses in 
beds tilted up almost everywhere at very high angles, with a general strike of N. 
28° E. 
In another contribution, referring to , the pegmatites of the island 
of Manhattan, Julien" shows that these exist in at least two series, of 
which the oldest is the more extensively intercalated among the folia- 
tion seams and is coincident with the strike. The later series, on the 
other hand, cuts the schist in various directions and inclinations. He 
adds: 
Some of the most prominent features are the results of pressure upon the original 
veins through orogenic movements of the stratum of schists, viz, fissuring, faulting, 
crushing, etc. 
ojulien, A. A., Nods on the origin of the pegmatfties, Manhattan Island: Sci< nee, n.ser., vol, 
1900, pp. 1006-1007. 
