SURVEY OF THE ISLAND OF NEW-YORK. 
593 
the gneiss to the depth of from one to twenty-five feet. The strata are exceedingly confused. 
In the southern part the strike is N 45° E, and dip 45° to 80° varying frequently 10° or 
20° in dip in forty or fifty feet distance. 
Columnar gneiss is seen in many places on the island, but in none more conspicuous than 
at the south entrance to the tunnel. The columnar structure of gneiss only occurs where the 
mica is replaced by hornblende. There is not the appearance of crystallization, as in basalt 
and greenstone ; but the fragments have the appearance of old logs, or like the half or quarter 
of a log, as if split and quartered by art. They are seen in the upper part of the cut, and 
vary their direction in the distance of a few feet. 
97th-street: East of the railroad the rock has been laid bare nearly one hundred feet, and 
develops drift furrows more than a foot wide and two inches deep. Direction N 45° W. 
Other rocks in vicinity are found to contain similar furrows, and in the same direction. This 
was evident on rocks freely exposed to the weather in many places within a few streets of the 
northern entrance of the tunnel. 
From 97th-street to 115th-street, including Harlem creek and the neighboring low grounds, 
the grading of the railroad is from ten to thirty feet above the natural soil. 
lOlst-street: The gneiss dips down below the surface, and does not appear again till we 
reach 115th-street. 
Between 115th and 116th streets, on the east side, found fragments of a radiated mineral 
in a vein in gneiss ; also epidote in veins in gneiss, but quite inferior specimens. Since found 
the radiated mineral4o be red stilbite, but the specimen was inferior, and could not be so 
satisfactorily determined as is desirable. 
118th to 120th-street, is a quarry of gneiss, which has been used to build a church, stand¬ 
ing within a few rods east of the railroad. ‘ This rock contains a considerable proportion of 
limestone. In some specimens the carbonate of lime composes half of the entire mass, and this 
rock in some places contains distinct crystals of calcareous spar, with some other varieties of 
crystalline form. The above quarry constitutes a portion of a cohical hill of some twenty to 
thirty feet elevation, which was opened by the railroad passing through its western half, by 
which a good section of the strata was developed. The strata were found to follow the slope 
of the hill. They were noticed by me at the time of opening the railroad, and a drawing 
made, as I considered the appearance interesting. 
120lh-street commences the last cut in rock before we reach the village of Harlem. Here 
the gneiss is well stratified. Strike N 45° E. Dip 45° W, and the cut twenty-five to thirty 
feet deep. The rock is inferior in quality, and has been in some places much disintegrated 
by pyrites. It contains veins of quartz and granite, and in a few cases rose quartz in veins 
of two inches wide were found under the bed of the railroad. 
Boulders of granular limestone were found when the road was first opened, fragments of 
which are still to be found in the drift beds on the side of the cut (east side). 
This last cut terminates at 124th-street, near the Harlem depot, and does not reappear 
Geol. 1st Dist. 75 
