590 
GEOLOGY OF THE FIRST DISTRICT. 
with 8th avenue, grooves are apparent almost the whole distance, but generally less distinct 
than those at the fortifications. 
A few hundred yards north of the new Lunatic Asylum, the rock exhibits most distinct 
and remarkable grooves for a distance of two hundred feet north and south, and from ten to 
thirty feet east and west. Strike N 25° E. Grooves N 45° W. 
Returning from the Hudson and Mohawk valley on the 8th avenue, we found abundance of 
greenstone boulders along the south border of the valley, and throughout almost the whole 
distance from Manhattanville to the avenue. 
As we ascend the hill on 8th avenue the gneiss makes its appearance. Strike N 30° E. 
Dip E 80° to 85°. Grooves abundant south of the rock. Direction N 45° W. 
Opposite the woods and south of the second rise from the valley, we find on the east side 
of the rock, well stratified gneiss. Grooves abundant, N 45° W. 
Again at 97th-street, and 80th to 98th-street, near the track, the gneiss is full of grooves, 
running N 45° W. Rock is on the level with the street. Strike N 30° E. Dip vertical. 
96th to 95th-street: East side, six feet above grading, covered with remarkable grooves. 
Direction N 45° W. Dip vertical. Strike N 30° E. These grooves are more remarkable 
than any I have seen to-day. 
95th to 94th-street: East side, well characterized gneiss, but rather tender, covered with 
iron rust from pyrites. Grooves N 45° W. Strike N 30° E. 
93d to 92d-street: East side grooves. Strike and dip as before. Again near the last, but 
a little south, say twenty rods, grooves on both sides very large and distinct. Direction N 
45° W. Strike N 30° E. Dip 75° E. The rock is uncovered north and south four hundred 
feet, and east and west from eighty to one hundred feet. 
86th-street, east side, forty feet north and south, and fifteen east and west; covered with 
grooves. Direction N 45° W. Strike N 25° E, and dip vertical. Again eastward in the 
fields, similar grooves. Direction N 45° W. 
84th-street: Similar rock and grooves in every respect like the last. 
84th to 82d-street, east side, the rock uncovered to a considerable extent; very tortuous 
and full of veins. The whole surface of the rock has been smoothed by abrasion, and the 
grooves are very remarkable, requiring a drawing, as well as the tortuosity. Direction N 
45° W. 
81st to 79th-street, on both sides of the way, but the grooves are more distinct on the east 
side. Direction N 45° W. The rocks are much elevated ; grooves are few, but large and 
deep. 
77th-street: Rock on the east side insulated, ten rods from the avenue, thirty feet above 
surface, one hundred and fifty feet long, and covered with grooves. Much weatherworn. 
Direction N 45° W. 
76th to 75th-street: Gneiss well stratified. Strike N 25° E. Dip 80° W. In state of 
rapid decomposition from pyrites. No grooves seen. 
68th to 69th-street: Gneiss more sound, and grooves N 48° W ; strike N 35° E, on the 
east side. Also on the west side grooves N 48° W. 
