either for a horizontal or vertical cut and side and top rounds. The
drillers were protected while at work by platforms of timber built out
from the floors of the compartments above. This plan, while probably not
quite as economical of explosives, saved nearly all the delay due to
drilling the bench.

[Illustration: PLATE LXX, FIG. 1.--SMALL SHAFT SUNK TO ROCK.]

[Illustration: PLATE LXX, FIG. 2.--BREASTING AND POLING IN FRONT OF
SHIELD.]

[Illustration: PLATE LXX, FIG. 3.--SHUTTERS ON FRONT OF SHIELD.]

[Illustration: PLATE LXX, FIG. 4.--HYDRAULIC ERECTOR PLACING SEGMENT.]

_All-Earth Section._--As described by Messrs. Hay and Fitzmaurice, in a
paper on the Blackwall Tunnel,[C] the contractor had used, with marked
success, shutters in the face of the shield for excavating in loose open
material. He naturally adopted the method for the East River work. When
the shields in Tunnels _B_ and _D_, at Manhattan, the first to be driven
through soft ground, reached a point under the actual bulkhead line,
work was partly suspended and shutters were put in place in the face of
the top and center compartments. The shutters in the center compartments
in Shield _D_ are shown in Fig. 3, Plate LXX, while the method of work
with the shutters is shown by Figs. 4, 5, 6, and 7, Plate LXVIII. Fig. 4
on that plate shows the shield ready for a shove. As the pressure was
applied to the shield jacks, men loosened the nuts on the screws holding
the ends of the shutters, and allowed the latter to slide back into the
working compartments. At the end of the shove, the shutters were in the
position shown in Fig. 5, Plate LXVIII. In preparing for a new shove,