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. 100, " " No. 200 " 8.0%
" No. 200 " 19.0%
------
100.0%

This means that grains of all but 4% of it were less than 0.0071 in. in
diameter. The 19% which passed the No. 200 sieve, the grains of which