56 TRANSACTIONS OF THE [Nov. 14, 
largest one that I have seen; although the contact is not shown, 
as building or street pavement hide it, there is a width visible of 
at least 100 feet. ‘That granyte may be segregated, or from no 
different source than the gneiss, is shown at 95th street and 
Fourth avenue where there is a boss or knob of granite, 6 ft. x 
4 ft. in gneiss, apparently an individual lump. Granyte also fills 
fissure-veins and cracks that run across the bedding at all angles. 
At Tenth avenue and 82d street, there is one 6 feet wide, rising 
15 feet above the street, and at the north end of T’enth avenue 
there is one 8 feet wide, almost parallel to the bedding and visi- 
ble from a long distance, as its white surface runs like a broad 
ribbon across the darker gneiss. Along the river path, south of 
High Bridge, there are several at a small angle with the strata, 
6 inches wide, but traceable for 50 yards or more. Some of the 
granite veins are very curiously and beautifully banded. Next 
the walls, on each side, is a stripe of mica whose crystals or 
leaves all point in towards the middle of the vein, while the 
interior is filled by the veinstone. This is not compatible with 
an eruptive filling, nor is the fact that the contact is everywhere 
sharply defined with no injury to the gneiss. 
The published descriptions of the island illustrate very well 
the change in the accepted geological idea of granyte. The pre- 
vailing opinion now is in favor of a metamorphic origin. But 
in the sections of the island, by Mr. Cozzens (1843), an interior 
of granyte is always represented as supporting the gneiss, and 
occasionally welling up through it as veins. 
The granyte varies sometimes to a pegmatite, and sometimes 
has its feldspar a plagioclase. The feldspar weathers to kaolin and 
the quartz drops away to sand. This is shown in a decomposed 
vein just over the Highth avenue park wall, a block or two below 
110th street. ‘There isa broad outcrop of a disintegrated and 
kaolinized vein, the solid portion being too deeply buried to be 
visible. 
Throughout the gneiss, particularly the micaceous variety of 
the east side, are found masses of a green plagioclase, presumably 
oligoclase, sometimes six to eight inches in diameter. It con- 
tains pyrite, calcite, and occasionally a well-formed crystal of 
tourmaline. Irregular deposits or segregations of orthoclase also 
run through the gneiss, varying from brick-red to lighter shade. 
It appears to fill the irregular, jagged cracks from disturbance. 
Tourmaline is very generally distributed through the granyte, 
often in large but very brittle prisms, and the mica occasionally 
is In very broad plates or leaves. 
Less Important Rocks.—A very curious and interesting rock? 
1 Mather’s Report, p. 582. 
