els
_A_ and _C_ were originally fitted with fixed hoods and fixed extensions
to the floors, as shown in Fig. 2, Plate LXV. A full description of the
shields will be found in Mr. Japp's paper.

The shields in each pair of tunnels were advanced through the solid rock
section about abreast of each other, until test holes from the faces
indicated soft ground within a few feet. As the distance between the
sides of the two tunnels was only 14 ft., it was thought best to let
Tunnels _B_ and _D_ gain a lead of about 100 ft. before Tunnels _A_ and
_C_ opened out into soft ground, in order that a blow from one tunnel
might not extend to the other. Work in Tunnel _C_ was shut down on
December 23d, 1905, after exposing sand to a depth of 3 ft. at the top,
and it remained closed for seven weeks. Work in Tunnel _A_ was suspended
on September 29th, 1905. By the time Tunnel _B_ had made the required
advance, it, together with Tunnels _C_ and _D_, was overtaxing the
capacities of the compressor plant. Only a little work was done in
Tunnel _C_ until July, 1906, and work in Tunnel _A_ was not resumed
until October 22d, 1906.

TUNNELS DRIVEN WESTWARD FROM LONG ISLAND CITY.

_Materials and Inception of the Work._--The materials met in Tunnel A
are typical of all four tunnels. From the Long Island shafts westward,
in succession, there were 124 ft. of all-rock section, 125 ft. of part
rock and part earth section, 22 ft. of all-rock section, 56 ft. of part
rock and part earth section, 387 ft. of all-rock section, 70 ft. of part
earth and part rock section, and 1,333 ft. of all-earth section.

[Illustration: PLATE LXVII]

The materials passed through are indicated on Plate XIII. The rock was
similar to that of the Blackwell's Island Reef, and was likewise covered
by a layer of sand and boulders. The remainder of the soft ground was
divided into three classes. The first was a very fine red sand, which
occurred in a layer varying in thickness from 6 ft. to at least 15 ft.
It may have been much deeper above the tunnel. It is the quicksand
usually encountered in all deep foundations in New York City. The
following is the result of the sifting test of this sand:

Held on No. 30 sieve 0.6%
Passed No. 30, " " No. 40 " 0.4%
" No. 40, " " No. 50 " 0.7%
" No. 50, " " No. 60 " 2.4%
" No. 60, " " No. 80 " 14.9%
" No. 80, " " No. 100 " 54.0%
" No