The restrictions on form imposed by barks such as elm, chestnut, and hickory were very great. These barks, which are not as elastic as birch bark, were sometimes employed in a single large sheet. The sheets were not joined for length; canoes of this material were often formed by crimping, or lap folding, rather than by cutting out gores and then sewing the edges together. The characteristics of these barks can readily be demonstrated with a sheet of paper: such a sheet can be made into a crude canoe-form by bending it lengthwise and joining the ends, but it will be obvious that the midsection takes a very unstable ~U~-form. By forcing the ends inward to give a ram, or chin, effect to bow and stern, a somewhat flatter bottom can be obtained in the midsection. By crimping or folding the paper gore-fashion near each end of the canoe-form at the gunwale edge, some rocker is created in the bottom and the width of the gunwales is increased near the ends, giving more capacity. But without the crimping along the gunwale, when the midsection form is flattened on the bottom, the latter tends to hog. Many of these bark canoes utilized both the rams ends and crimping to obtain a more useful form. However, while a sheet of birch bark could be crimped or gored into a scow-form canoe such as the Asiatic birch-bark canoe, no example of this form from North America is known. On this continent all bark canoes were sharp at both ends, i.e., double-ended, although a number of North American dugouts were scow-(or punt-) shaped. [Illustration: Figure 22 CANOE formed (a) without crimping or goring sides, showing hogged bottom; and (b) with ram ends to reduce hogging of bottom.] [Illustration: Figure 23 CANOE formed (a) by crimping sides, showing rockered bottom line, and (b) by simple gores in sides. The same effects are obtained by making bark cover of three pieces: sides and bottom.] Birch bark gave much more freedom in the selection of form simply because it could be joined together in small odd-sized sheets to shape a hull, and because it was elastic enough to allow some "moulding" by pressure of the framework employed. Birch bark could be gored, or slashed, and rejoined without resort to folding or crimping; thus it permitted a smooth exterior surface to be achieved. The toughness of the bark was sufficient to allow some sewing in line with the grain, to add to the width of a sheet, if the proper technique were employed (this was also true to a lesser extent of spruce bark). [Illustration: Figure 24 CANOE FORMED by use of gores and panels.]