Union Cavalry Colonel <a href="https://en.wikipedia.org/wiki/Benjamin_Grierson" class="extiw" title="en:Benjamin Grierson">Benjamin H. Grierson</a> (seated with hand resting on chin) and staff.
Lytle Photography
File from <i><a rel="nofollow" class="external text" href="https://archive.org/stream/photographichist04mill#page/n138/mode/1up">The Photographic History of The Civil War in Ten Volumes: Volume Four, The Cavalry</a></i>. The Review of Reviews Co., New York. 1911. p. 138.