I've been studying train routes for Sam's trip to St Louis in March of
1867.  Explanatory notes at the Mark Twain Project and David Fears' Day
By Day report that he departed New York on the New Jersey Central.  It
took two days to get to St Louis but the New Jersey Central would go no
further than Easton, Pennsylvania.  I've made an attempt at figuring
out a route using the train route files from the University of
Nebraska.  They have kmz file for 1861 and 1870 - it's amazing how much
growth in railroads there was between those dates - not to mention the
difference with Sam's first journey to New York in 1853.

Anyway, for any railroad historians out there, take a look at this and
let me know what you think...

https://twainsgeography.com/content/new-york-st-louis-march-1867