tunnel, and a typical cross-section is shown on Plate XII. The tunnels
continue on tangents under the streets to Second Avenue where they curve
to the left by 1° 30' curves, passing under private property, gradually
diverging and passing through shafts just east of First Avenue. About
350 ft. west of the shaft, the divergence of the two lines from each
street becomes sufficient to leave a rock dividing wall between them,
and thence eastward each tunnel is formed in a separate excavation. A
typical cross-section of the two separated tunnels is shown on Plate
XII.

It thus appears that eastward from the station the lines constitute a
four-track railroad, each track being in a separate tunnel; for
convenience of the work these lines were designated _A_, _B_, _C_, and
_D_, from north to south.

[Illustration: PLATE X.--Manhattan Shaft, Lines _A_ and _B_]

At an early date, when the organization of the engineering staff was
taken up, Charles L. Harrison, M. Am. Soc. C. E., was appointed
Principal Assistant Engineer. He was directly in charge of all parts of
the work, and all Resident Engineers reported to him. George Leighton,
M. Am. Soc. C. E., was placed in charge as Resident Engineer of the 33d
Street lines from the west end of the three-track tunnel to the shaft
and also eastward from the shaft under East River. As he was not then
able to endure the effects of compressed air, the work under the river
was transferred to James H. Brace, M. Am. Soc. C. E., as Resident
Engineer. Before the completion of the land tunnels under 33d Street,
Mr. Leighton accepted more responsible employment elsewhere, and Mr.
Brace assumed charge of them also. Francis Mason, M. Am. Soc. C. E., was
in charge as Resident Engineer of the 32d Street lines during their