There were three Marshalls in Co. F of the 4th Ky. Inf. CSA, but none of them were named John - there were Henry, Richard, and Samuel.

John L. Marshall was Sgt. Maj. of the 4th Ky. Inf. CSA, but he died in 1913 and is buried in Cave Hill Cemetery in Louisville.

I think your ancestor was likely Pvt. John J. Marshall, Co. F, 40th Ky. Inf. USA. You can look him up on the Civil War Soldiers and Sailors System, http://www.itd.nps.gov/cwss/soldiers.htm .

Geoff Walden