The description is for canoes of minimum finish; builders often used split and shaped gunwales, split ribs, and splint sheathing if these could be prepared during the winter. The construction of a skin canoe was not a specialized process in which a hunter consistently built this one type; the selection was determined by natural conditions. If he were to come out of the woods too early in the spring to make the construction of a spruce-bark canoe easy, then he would resort to skin construction; the statements of old Malecite hunters leads to the conclusion that as emergency craft they used spruce-bark canoes most often. Perhaps the most primitive of the skin boats built by the North American Indian was the so-called bull-boat of the Plains Indians. These were not canoes but coracles--bowl-shaped and suitable only for use on streams, where ferrying would be the main requirement. The boats were covered with buffalo-hides and their framework was usually made of the willow shoots found along the streams. The framework followed, to some extent at least, the basketwork principle, a circular gunwale or rim being used. The ribs were set in two groups, half at right angles to the other half in very irregular fashion. This construction formed a sort of rough grating in the bottom. The ribs were lashed together with rawhide and apparently the craft was built up on the skin as were the Malecite skin canoes. Battens in circular form were used on the sides to fair the cover. The form of the bull-boat varied somewhat among individual builders; sometimes it assumed almost a dish shape with shallow flaring sides, but more commonly the sides were nearly upright; the bottom was always flat, or nearly so. These bull-boats appear always to have been small. Judging by the examples preserved, a bull-boat 5 feet over the rim or gunwale, or made of more than one skin, was extremely rare, and most examples are nearer 4 feet and built on a single skin. Many were too small to carry a person; these were intended to be loaded with cargo to be kept dry and towed by a swimmer. When they were large enough to be paddled, the paddler worked over the "bow," as in a coracle. Probably all the Plains Indians living near streams once used the bull-boat, but existing records show only the Mandan, Omaha, Kansas, Hidatsa, and Assiniboin to have used it. The Blackfoot (Siksika) and Dakota are said to have used some kind of a skin boat in which their tepee poles were employed as a temporary frame, but nothing is recorded of their form.