522 
GEOLOGY OF THE FIRST DISTRICT. 
A considerable part of it is still covered with its native forests, though most of it is capable 
of tillage. The southern part extending northward as far as the ten-mile stone, taken as a 
whole, is more level than the northern ; but from the ten-mile stone to the northern extremity, 
it may be considered as divided into three sections, the western, the middle, and the eastern. 
The western is a continuous ridge of gneiss from a quarter to half a mile in width, and 
from sixty to one hundred feet above the waters of the Hudson. The middle is a long narrow 
valley, commencing a little narth of the ten-mile stone, continuing northward to Kingsbridge, 
and descending most of the way ; it is in this valley the great Kingsbridge road passes. This 
valley is lined abundantly with boulders of sandstone, greenstone, and white limestone like 
that from Kingsbridge, with large quantities of sand and loam. On the western side of 
this valley the rocks of the western ridge are very precipitous, being in many places fifty'Ot 
sixty feet perpendicular. The third, or eastern section, lying directly east of the Kingsbridge 
road, and nearly parallel with it, is a ridge of gneiss of some elevation, though inferior to the 
first or western ridge ; and is covered to a very considerable depth on its western slope with 
transported materials, in which diluvial loam and boulders of greenstone and white limestone 
are most numerous, though many other varieties are to be seen. The eastern face of this ridge 
is precipitous, and borders on Harlem river or the intervening marshes. It-is lower and 
shorter than the western, dipping down below the surface in the vicinity of IQSth-street and 
the Tenth avenue. 
“ From the 198th to 204th-street, on the Kingsbridge road, a narrow valley is formed by 
an opening through the western ridge, and extending 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 eastern 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 east¬ 
ern slope of the ridge, the limestone generally called Kingsbridge marble commences, 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, be¬ 
coming 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 limestone. At the,junc- 
tion 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 fifty to eighty yards in width, 
and about one hundred yards west of the road, the strike is N. 30° E., and the dip vertical. 
It is flanked on both sides by gneiss, and as it continues northerly in the direction of the strike 
