H. A. Hall and "Darky". He has a stockwhip in his right hand. Notice how they ride "long" in the stirrups.
This is Aubrey when he was quite old — he rode until he was 80. Note the water bags on the horses necks.
Also on Commons: <a href="https://commons.wikimedia.org/wiki/File:Harold_Aubrey_Hall_riding_" rel="noreferrer nofollow">commons.wikimedia.org/wiki/File:Harold_Aubrey_Hall_riding_</a>(cropped).png