600 
GEOLOGY OF THE FIRST DISTRICT. 
Crossing the creek west side of M^Comb’s dam, examined the rock, which again appeared 
within one hundred rods northwest, about un the line with .9th avenue. Coarse, inferior gneiss, 
without veins-. Strike N 35° E. Dip vertical. 
162d-street at 10th avenue; On Madame Gemmel’s place the rock appears on the surface, 
and is covered with grooves. Direction N 45° W. They are very distinct at the Porter’s 
lodge, south side ; also within the yard and enclosures. Strike N 30° E. Dip vertical. 
Again about half a mile northward, at the ten-mile stone on the Kingsbridge road, a few 
rods north, and again a few rods-south of the stone, drift groovesvery.numerous and ^distinct. 
Direction N 35° W. Strike N 30° E, and dip vertical, 
186th, 187th and 188th streets : Still on the road, and west of 11th avenue and east of 
12th avenue. Here are boulders of greenstone, granite and white marble, like that of Kings¬ 
bridge ; the rock not seen in place at this spot. Here or a little south of the place, the island 
seems to divide longitudinally into the western and eastern ridge, elevated from sixty to one 
hundred feet above the Hudson and East rivers, or the contiguous waters, with an intervening 
valley extending to the village of Kingsbridge, and descending most of the way thither. The 
western ridge continues to the north end of the island, while the rock.of the eastern dips 
down and disappears near 195th-street and 12th avenue, which is considerably east of Kings¬ 
bridge road. 
From 195lh to 197th-street, there is an opening through the western ridge, forming a con¬ 
tinuous valley from the Hudson to the Spuytenduyvel creek (or East river where it approaches 
Kingsbridge). Through this valley, vast masses of drift in form of loam, sand and gravel, 
have been carried and piled up in conical hills east of the road, and on the northern slope of 
the eastern ridge, which also contains abundance of boulders of marble, granite, greenstone 
and sandstone. 
At the northern part of this valley, and from thence to Kingsbridge, the road continues-on 
the east of the ridge, and in view of the East river, leaving all the high grounds on the west. 
It is at this northern portion of the valley, and on the eastern - portion of the.ridge, that the 
limestone, called Nichol’s quarry, begins, and continues to the. northern extremity of the 
island, a distance of a mile or a mile and a quarter. Here .the-limestone has been opened for 
marble. The quarry belongs to a Mr. Thompson, who resides at Yonkers. Most of the 
material obtained from it hitherto has been used, and is now being used, to macadamize the 
roads in the vicinity. The marble is. of two varieties, coarse granular white or yellowish 
white, and compact white or bluish. This quarry is the last opened in this neighborhood, 
about a year ago, and is forty to fifty feet deep on north side, and extends into the side hill 
about the same.distance, and on a level with.the bottom of . the valley. 
The marble is, taken as a whole, rather inferior ; seems to be a part of the gneiss forma¬ 
tion, with only a change in the mineral matter; for at the junction of the two, and often for 
a considerable distance in the marble, it continues the -structure of gneiss ; and this is almost 
always the case where the mineral matter of the, gneiss commingles with the marble, but 
wherever the material becomes a pure limestone, it then lies in beds, almost without stratifi- 
