This is from an interesting collection that took a lot of work, the photographs were about 3" square, very thin paper and badly faded, circa 1860's
More research on the troops in the picture is required, I'm guessing they are British, the odd style helmets were worn by some British mounted units.
The guns in some of the pictures are short, possibly Enfield Muskatoons a type used by the British army starting in 1861, it was also used by both sides during the US Civil War.