Since this thread has been 'bumped', I have a note (that requires some amplification or confirmation from someone like Johnny Degges who knows the full details).
It was noted early on that the bridge crossings from St. Louis south are at high level. Something I would note is that, in the Memphis area, when ferry crossings were used prior to 1892, railroads terminated to the northwest of the city, where the approach is low-grade almost right to the river (indeed, right to the river at its right 'stage') whereas the present bridges are at the top of the 'bluffs' considerably south, near the elevation of both Central Station and the site of Union Station, where the high-level crossing involves little elevation change on the east bank. Several of the ROWs to the ferries still survive, either in truncated operation or as visible traces of track or grading.