John Henry Worsham (8 July 1939-19 September 1920)
The title of his memoirs was: One of Jackson's Foot Cavalry his Experience and what he saw During the War 1861-1865, Including a History of "F Company," Richmond, Va., 21st Regiment Virginia Infantry, Second Brigade, Jackson's Division, Second Corps, A. N. Va. https://www.findagrave.com/memorial/27011277/john-henry-worsham
Edit - Sorry, Virginia Dave, Douglas is not the correct answer here. He did write a memoir titled "I Rode with Stonewall," but he belonged to the 2nd Virginia, not the 21st, and he did fight at both Chancellorsville and Gettysburg.
Welcome to the trivia game, anyway. Hope you'll come back and play again.
You probably noticed the question has been a duplicate - or you at least found it sounded somewhat familiar. My apologies! After I first sent in the question, I noticed a mistake and sent Ami the correction. Since the corrected question was amidst more submitted trivia questions, I confused Ami. I apologize. Feel free to throw things at me; I only ask that you use something soft.
PS: Hoosier, if you let the question stand, feel free to not give me the credit points. I don't deserve them.
Edit - The question did seem vaguely familiar, but I still had to make an effort to find the answer, so I considered it a worthwhile question and I will give you the ten points. I do appreciate your honesty.
This does not, of course, constitute an open invitation for players to consciously resubmit questions that have been used before.