592 
GEOLOGY OF THE FIRST DISTRICT. 
Fourth Avenue. 
The 4th avenue commences at 14th-street, or at Union place. The natural seal is, in this 
vicinity, fifteen to twenty feet above grading, and consists of drift, being an exceedingly 
confused mass of loam, gravel (last rare), and boulders of immense size, some of which are 
ten to sixteen or eighteen feet in diameter. Below grading, in many places, the drift loam 
continues some feet downward, say six to ten, when, if we do not reach the rock, we find a 
fine sand, not generally white, but of a dark grey, and often containing much mica and grains 
of hornblende, with quartz and felspar predominating, and indicating that a considerable por¬ 
tion of it had been the result of the disintegration of granite and gneiss. 
At the corner of 16th-street and 4th avenue, the gneiss, east side of avenue, appears on a 
level with grading. Strike N 25° E. Dip W 80°. 
18th to 19th-street, patches of loam remain, ten to fifteen feet above grading, with sand 
here and there, at and below grading. 
20th to 21st-street is Grammercy park on the east, towards the 3d avenue, and open 
grounds either side of 4th avenue. On 21st-street, a few rods from the avenue, is a large 
boulder of hydrous anthophyllite of a peculiar character, differing somewhat in appearance 
from that already referred to. It is of a dark or greenish color and spongy texture, but only 
on the outside ; for, on breaking it open, it is compact within, and has indications of limestone 
and other minerals differing in character from any seen at the locality examined. 
25th-street, and twenty-five rods west of the avenue, gneiss appears at surface of grading. 
Strike N 30° E. Dip 75° W. Drift furrows. Direction N 25° W. Here is an immense 
boulder of the hydrous anthophyllite, twelve feet long, eight broad and six high, with abun¬ 
dance of longitudinal grooves on its surface. 
31st to 32d-street is Sunfish pond, filled up to the level of grading. 
32d-street: The rock, which is compact gneiss, appears above the surface, and ten or fifteen 
feet above grading. Here commences the cut in the railroad, and where the cars, going from 
the city, exchange horses for steam power. Strike of the gneiss N 25° E. Dip 80° W. 
The dip varies as we go north, and the rock differs considerably in texture. In some places 
the dip is 45° W. The first cut of continuous rock ends at 37th-street. 
38th to 40th-street, the rock (inferior gneiss) appears, and from 42d-street onward the grade 
level is from one to ten feet above the natural soil, and this continues to 47th-street. 
47th-street: Another cut commences ; fifteen feet in the deepest place, reaching the rock, 
and extending to 50th-street. The soil is drift loam. 
53d-street: Rock (gneiss) appears on the east side. Dip 45° W. Strike N 25° E. 
66th to 72d-street: Cut ten to thirty feet in drift. 
72d to 79th-street: Valley twenty to thirty feet below grading. 
79th-street crosses from the East river to 5th avenue, when it terminates in the west. 
From 79th-street to the tunnel, the grading is done nearly all the way by cutting through 
