Can someone tell me what a hemlock wall is? I know what a hemlock is, and I know what a wall is, but I can't picture a hemlock wall ...

The clump of weeping-willows about the duck pond, and the
Norway spruces in front of the Hatchard gate, cast almost the only
roadside shadow between lawyer Royall's house and the point where, at
the other end of the village, the road rises above the church and skirts
the black hemlock wall enclosing the cemetery.

(Edith Wharton - summer)

Is it just a row of fir trees around the cemetary?