Bruce,
Thanks for finding that reference to the H&TL incline superintendent. That does confirm that the incline originated with the construction of the rest of the railroad. The account of the gage mistake given by Alexander Agassiz makes it sound as if they began construction of the railroad with the incline and worked westward to the mine.
I have been looking at your references to the sizing in track cross section, and I don’t quite understand the “check gage” specification in either practical purpose or in the terminology.
I notice that the SSMRS shows the “check gage” dimension from the gage line on one side to the outside of the guardrail on the opposite side. Whereas the NMRA shows it as the gage line on one side to the back of the wheel on the opposite side.
Regarding terminology, the term “check gage” confuses me because this dimension is not track gage. One of the diagrams shows a tool or gage used for checking a variety of dimensions. So does check gage refer to a gage used as a tool to check dimensions; or does it mean to inquire as to what the gage measurement is?
Regarding the purpose, why would a person want to know this dimension? I can see the need for wheel profile dimensions, gage, and back-to-back. Gage is easy to measure on the rails, but not on the wheels because if falls in space relative to the wheel flange contour. Back-to-back is easy to measure on the wheels. So this “check gage” dimension would be easy to establish on one end and nearly impossible to establish on the other end.