This is an interesting Civil War Union GAR (Grand Army Of The Republic) Unidentified Veteran and member of The Alexander Hays Post No. 3, with the brass numeral 3 on his cap. He wears the full uniform of the G.
A great dark red-brown Cabinet Card Photograph by Photographer Charles Matt, at NO. This one is a larger size at 6.5" by 4.25" in dimension and bevel-edged with a gold edge. Judging by the Veteran's still very youthful appearance, this likely wasn't made too long after the war. Additionally, a search for that location shows a number of other photographers operated at that same address. Excellent condition with great clarity of this proud looking Civil War Veteran.