I don't mean to necropost on an almost 2 year old topic, but I ran across this map while I was researching some other stuff and I figured I'd provide some answers about the "old alignment" in question at Rock Glen. Refer to
this map.
There was in fact a spur to "American Electrolytic Co" (ie, a salt processor of some kind, I'm guessing) from both Erie and BR&P, and as lvrr325 mentioned, this shows up on Topos up to
1932 prior to what is now Rt 19 being realigned.
As lvrr325 also mentioned, the current and same alignment for the Erie main is shown all the way back to 1905 topos. In fact the only even remote reference on the topo maps that I can see to an old alignment for the Erie is in the
1944 topo after the NY 19 realignment where a broken line is shown through the area, and then nothing until the
1974 topos where they apparently re-evaluated the contour lines and you can see one cut in the 1350' line just south of the pipeline.