Your cousin was an interesting man. Here's some information on him:
Thomas C. Marshall was born in Oak Hill, Fauquier County, Virginia, on January 17, 1826. He was the grandson of the great Chief Justice of the United States Supreme Court, John Marshall. Not surprisingly, he studied law in Winchester before the war. Marshall was commissioned as a captain and served as a volunteer aide to Stonewall Jackson at the First Battle of Bull Run in July 1861. He was appointed major of the 7th Virginia Cavalry June 20, 1862. He was captured during the August 2, 1862 Battle of Orange Court House. After he was exchanged after being captured at Orange Court House, he was promoted to lieutenant colonel on October 30, 1862. He fought in the Battles of Brandy Station and Trevilian Station, among others, and was wounded twice, at Ream's Station and Petersburg. He had six horses shot out from under him during the war. He was killed at Nineveh in the Shenandoah Valley on November 10, 1864 and was buried in Stonewall Cemetery in Winchester, Virginia.
I have done quite a bit of work on the 7th VA Cavalry over the years, so I have crossed paths with him numerous times. Marshall was a good soldier.