I suspect that the soldier in the photograph is not G.S. Davis, but that this is the name of the photographer, grandiosely termed an ‘artist’ in the inscription. Studio photographers of this era frequently referred to themselves as artists for marketing reasons to elevate their craft to the level of fine art.
I believe the photographer was George S. Davis, who is historically recognised for portrait photography during and after the Civil War. He operated a photography studio out of Clarksburg, catering heavily to soldiers passing through West Virginia by producing cartes-de-visite or CDVs (small, affordable, mass-produced photographs that could be sent home to soldiers’ families) but he also produced archival work such as a formal portrait of the historian Virgil Anson Lewis.
The uniform the guy in the picture is wearing appears to be a double-breasted coat with rectangular shoulder straps, typical for a higher ranking officer in the Union Army (as opposed to collar insignia worn by Confederate officers). It looks as if there is a single star on the shoulder strap (?) which would be for a Brigadier General.
Although there is some resemblance, I can’t convince myself that it’s Joseph Andrew Jackson Lightburn (not ‘Stonewall’ Jackson) who was commissioned as a Brigadier General of Volunteers by Abraham Lincoln in March 1863.
Approximately 300 to 350 individuals served in the Union Army with that rank.