Several have mentioned the conditioning on the trail, made me think of this journal -
The 3rd Iowa Inf. left Memphis just before noon, 6 Sep '62, after being stationed there about 6 weeks.
Sgt Will Newlon logs: "Marched 9 miles where we now rest for the night. The march was very hard on the men as they have not marched very much for more than a month."
Will points out challenges affecting travel time: "Our regiment is the rearguard of the division today, which decidedly is the hardest place to march in a division. The division train (about two miles long) was immediately in advance of us and some of the teams were continually balking, breaking down bridges &c which made it very tedious indeed."
They proceed to march 16-17 miles a day for the next 7 days (except for 1 day off to build a bridge). They have a 24 mile day a bit later in the month, and march well over 20 again on Oct 4 - the day before fighting the Battle of Hatchie Bridge (where Newlon loses a leg).
Tim