No. 275.] 
183 
the western, clipping down below the surface in the vicinity of 198th^ 
street and the 10th avenue, 
From the 198th to 204th-street, on the Kingsbridge road, a narrow 
valley is formed by an opening through the western ridge, and extend- 
ing from the Hudson to Harlem river, in a northwest and southeast 
direction. Through this valley vast masses of diluvial loam and gravel, 
with sand and pebbles and boulders, have been transported and piled up 
in conical hills east of the road, and on the northern slope of the east- 
ern ridge, which is covered by abundance of boulders of limestone, 
granite, greenstone and sandstone. 
At the northern part of this valley, and from thence to the northern 
extremity of the island, the road continues on the east side of the ridge, 
and in view of the East river, leaving all of the high grounds on the 
west. At this northern portion of the valley, and on the eastern slope 
of the ridge, the limestone generally called Kingsbridge marble com- 
mences and continues to Kingsbridge, a distance of nearly a mile and 
a quarter. This marble, which has been chiefly wrought for burning 
into lime, is mostly of the variety called granular limestone, and is so 
loose in texture that after exposure for a time to the weather it falls to 
^pieces, becoming a kind of calcareous sand. It belongs to the gneiss 
formation, as is evident from the commingling of the two in many 
places throughout the course of the limestoiie. At the junction of the 
two rocks, and often for a considerable distance into the marble, it 
retains the structure of gneiss with the mineral matter of limestone- 
but where the matter becomes pure limestone, it lies in beds without 
stratification, or but obscurely stratified. 
At the southern limit of the limestone, where it is from 50 to 80 
yards in width, and about 100 yards west of the road, the strike is 
north 30° east, and the dip vertical. It is flanked on both sides by 
gneiss, and as it continues northerly in the direction of the strike or 
bearmg of the strata, it widens until it becomes from 400 to 600 yards 
in width, and from 10 to 30 feet in height, forming a low lidge imme- 
diately west of the road, but east of the main ridge of gneiss which 
flanks the eastern shore of the Hudson, and which terminates at Tubby 
Hook, about half a mile north of the commencement of the limestone. 
As the gneiss runs out at the mouth of the Spuytenduyvel creek, the 
whole ridge northward is limestone, the form and extent of which may 
be learned by inspecting the map of the island, where it is encircled in 
pencil mark. The strike was examined in a number of places on the 
