1895. ] NEW YORK ACADEMY OF SCIENCES. 275 
a few little zircons. This rock continued for 321 feet from the 
west shaft, except that it was at times a little harder or softer, 
and had an oceasional seam that was wet. At this distance the 
following section was met. 
9 ft. soft kaolinized pegmatite, of the consistency of 
cheese, but with vertical lines of garnets and biotite. 
5 in. quartz vein. 
6 ft. kaolinized pegmatite. 
8 ft. soft green chlorite schist, 7. e., decomposed mica 
schist. 
6 ft. green chlorite scales, with quartz nodules. 
Total, 29 ft. 3 in. 
The next 80 feet were firmer but were still of much decom- 
posed and chloritic mica schist. The following 98 feet were 
as follows: 
T ft. white kaolinized pegmatite. 
5 ft. soft black mud with lumps of lignite, which with the 
next seven feet evidently filled a fissure. 
2 ft. coarse river sand with abundant pyrites. 
5 ft. sand and black mud with lignite and balls of pyrites. 
22 ft. white kaolinized pegmatite with lumps of fcetid 
quartz. 
4 ft. do, streaked with chlorite. 
11 ft. kaolinized pegmatite. 
42 ft. soft green chlorite schist. 
Total, 98 ft. 
Samples of this white clay and green chlorite were sent to me 
when first penetrated because their close superficial resem- 
blance to the Cretaceous Amboy fire clays and overlying green 
sands gave rise to the suspicion that a remnant of the Creta- 
ceous had remained in the bottom of the East River, but a mo- 
ment’s close examination showed the fallacy of the supposition. 
It was in this section that the chief difficulties in tunneling were 
met. The firmer rock to the east came in at an angle of 45°, 
and after some rather unsound schist passed into the solid rock 
of Blackwell’s Island, This is a gray gneiss much like that at 
the north end of Seventh avenue and near 150th street. At one 
place 150 to 250 feet east of the west shore line of the island it 
proved to be under great strain, so that from time to time, even 
six months after the tunnel was opened, it cracked with re- 
ports like # pistol shot, and at intervals masses fell from the 
roof. It was also a very hard rock to drill. At 260 feet from 
