side. The original blanket was of material advantage, but the depth of
clay was insufficient to stop the loss of air.

The essential parts of the shields in the four tunnels were exactly
alike. Those in Tunnels _B_ and _D_, however, were originally fitted
with sectional sliding hoods and sliding extensions to the floors of the
working chambers, as shown by Fig. 1, Plate LXV. The shields in Tunnels
_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