They were canvas and leather shoes used in both armies. They may have differed slightly but they were worn. Note the following text and picture which was posted on another forum:
"CANVAS SHOES FOR THE ARMY. - We learn at the Quartermaster General Department that there have been received there 5000 pairs of a new kind of shoes, of a rather curious description, that promises to answer [word is obscured] in the great scarcity of shoe leather. The upper portions of the shoe are made of canvas instead of leather. The canvas is prepared so as to make it impervious to the weather, and is said to equal in comfort, durability and all respects of wear, the best shoe leather." - Richmond Enquirer
Shown is a picture of Union soldiers wearing canvas and leather shoes.