Vintage Dunhill Two Tone Belt Buckle with leather belt

Seems to be a unique design, can't find any like it. Don't know purpose of the snap button on the belt and the adjacent hole. See pictures for the condition of the buckle and belt. Buckle size is: 1 5/8 inches by 1 1/4 inches by 5/8 inches. Belt is 41 inches. Back of belt hard to read. Size 34. Soften cowhide. TownCraft. xxxx-it-stretches. 4775.