g32 ANNALS NEW YORK ACADEMY OF SCIENCES 



with good prismatic cleavage, dark reddish brown biotite and feldspar. 

 The feldspar is mostly plagioclase, giving extinction angles up to 16° 30' 

 in sections at right angles to the albite lamellae. It is probably andesine. 

 A little microcline is also present. Much of the feldspar has been altered 

 to an aggregate of kaolin, sericite and quartz. Inclusions of biotite occur 

 both in the feldspar and amphibole, especially in the former. Apatite, 

 magnetite and a little titanite are present as accessory constituents. A 

 little pyrite forms an introduced mineral. In the edge of the mass, the 

 rock becomes very much finer grained. In thin section, however, one 

 still finds the granitoid texture. About equal amounts of light green 

 hornblende and dark brown mica are present. The other important con- 

 stituent is a plagioclase feldspar, evidently andesine, as it gives extinction 

 angles up to 20° 15' in sections at right angles to the albite lamellae. 

 Some orthoclase also occurs, together with minor amounts of apatite, 

 titanite and magnetite. 



Several other occurrences of diorite were observed in the area south 

 of Bedford. Sheets of hornblende schist are also quite numerous in this 

 vicinity, and the evidence again indicates that the intrusion of basic 

 igneous rocks took place at more than one period. 



Serpentine 



Serpentine is associated with the Manhattan schist at several places 

 in the area under discussion. These areas of serpentine are very similar 

 to the massive basic intrusive rocks just described, both in their mode of 

 occurrence and in their relations to the mica schist. D. H. Newland/^ 

 who has made a rather detailed study of them, has shown that they were 

 derived from basic intrusives, probably peridotites, which have undergone 

 serpentinization . 



The largest of these serpentine masses underlies the northern portion 

 of Staten Island. Smaller areas occur at Hoboken, New Eochelle and 

 Rye. Newland, in his study of the Staten Island serpentine, came 

 across unaltered remnants of olivine in some of his sections, showing that 

 the serpentine was derived from an olivine-bearing rock. The writer has 

 also noticed similar remnants of olivine in several sections from this lo- 

 cality. A thin section of the dark green massive serpentine from near 

 the northern end of the area at Eye was also examined under the micro- 

 scope. It consists of antigorite, bastite, some calcite, iron oxides, a very 

 little tremolite and a few remnants of unaltered olivine, with a green 

 spinel or pleonaste and magnetite as minor accessories. The bastite was 



*o School of Mines Quart., Vol. XXII, pp. 307-317 and pp. 899-410. 1901. 



