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TRANSACTIONS OF THE [may 20 
Ss 
~- 
interesting facts regarding local geol- 
ogy. By the courtesy of Mr. Charles 
M. Jacobs, the chief engineer of the 
work, the writer has had the oppor- 
tunity to visit the tunnel and collect 
a series of specimens. The profile of 
the tunnel published with Mr. Jacobs’ 
report to the East River Gas Company 
has furnished the outline of the figure 
here given, which, so far as the reduced 
scale admitted, is in true proportions. 
The tunnel is 2516.4 feet from shaft 
center to shaft center, and about 10 
feet 6 inches in diameter. Its roof is 
about 106 feet below mean low water. 
The difficulties in the way of soft 
ground and the influx of river water, 
which were overcome, make the enter- 
prise an exceptionally creditable one 
to those in charge. The worst of 
these were met under the west channel 
of the East River and were caused by 
weak and rotten seams of rock, and 
one old crack filled with river mud 
and sand, that at one time opened up 
the tunnel to visits from live crabs. 
In its engineering relations the tun- 
nel is of special interest because the 
softest ground was penetrated with the 
air pressure at 48 pounds, which is the 
highest yet used in work of this char- 
acter. It necessitated only 14 hours 
working shifts with an hour between 
each of rest outside the lock, and only 
45 hours working time for each man 
daily. The accompanying section il- 
lustrates the geology. Beginning on 
the New York side the rock is a thinly 
laminated mica schist, much contorted, 
but with a well marked general dip of 
about 80° west. A few small pegma- 
tite stringers are met. Under the mi- 
croscope the rock is seen to consist of 
biotite, in parallel scales, of quartz, 
orthoclase, plagioclase, magnetite and 
