Layers and Layers

From the NYPL photo album of the construction of the original IRT subway, “33rd Street & 4th Avenue” from January 3, 1901:

The big stone building on the right is the 71st Regiment Armory, which covered the block on the east side of Fourth Avenue between 33rd and 34th Streets. This is the old 71st Regiment Armory, which burned down in 1902, to be replaced by a larger building in pretty much the same fake-castle style. I know we’re looking north up Fourth Avenue for several reasons, the easiest of which to explain is the (now long gone) Unitarian Church at the northwest corner of 34th and Fourth on the left.

The street car in an open cut is heading into or coming out of the Murray Hill tunnel that was originally a route for New York Central trains to head south, and was switched to street cars when steam engines were banished to north of 42nd Street. The new subway tunnels went below that tunnel. Meanwhile, note the man on the right is standing on a wood surface with two sets of tracks on it. That’s the temporary street surface over the IRT excavation, and the tracks are for streetcars that are not continuing north of 34th Street. Apparently no one felt the need to have a temporary sidewalk at that location, since you could access the Armory from 33rd Street.

So there was a permanent, as yet unused subway tunnel, with a permanent in-use streetcar tunnel above it, and a temporary in-use set of streetcar tracks above that.