The Australian Cattle Dog (ACD), or simply Cattle Dog, is a breed of herding dog originally developed in Australia for droving cattle over long distances across rough terrain. This breed is a medium-sized, short-coated dog that occurs in two main colour forms. It has either brown or black hair distributed fairly evenly through a white coat, which gives the appearance of a 'red' or 'blue' dog. In the 19th century, New South Wales cattle farmer Thomas Hall crossed the dogs used by drovers in his parents' home county, Northumberland, with dingoes he had tamed. The resulting dogs were known as Halls Heelers. The ears are pricked, small to medium in size and set wide apart, with a covering of hair on the inside. The neck and shoulders are strong and muscular; the forelegs are straight and parallel; and the feet round and arched, with small, sturdy toes and nails. Australian Cattle Dogs were bred to drive cattle, but are also used to herd sheep.