It is obvious that much time and work could be avoided by use of a single large sheet of bark that was reasonably flexible and strong. But many of the barks meeting this specification had a coarse longitudinal grain that split easily, so forming a canoe by cutting gores was out of the question. This difficulty was avoided by folding, or "crimping," the bark cover along the gunwales at two or more places on each side of the canoe; this permitted the bottom to be flattened athwartships and the keel line to be rockered, both desirable in a canoe. The problem of closing the ends also had to be solved. This was done by clamping the ends of the bark between two battens and, perhaps, a bark cord as well, and then lashing together the battens, bark ends, and cord with wrappings of root thongs. Cord made from the inner bark of the basswood and other trees could also be used for this purpose. The ends of the canoe could then be made watertight by a liberal application of gum or tallow, while grass, shavings, moss, or inner bark mixed with gum or even clay could be used to fill the larger openings that might appear in hurried construction. Obviously, a simple wood structure was required by the specifications. Therefore, the gunwales were usually made of saplings with their butts roughly secured together or spliced. This allowed length to be obtained without the necessity of working down large poles to usable dimensions, a laborious and time-consuming undertaking with primitive tools. The thwarts were commonly of saplings with the ends cut away so that the thin remainder could be wrapped around the main gunwales and lashed underneath the thwarts inboard. Ribs were usually of split saplings, but there is some evidence that in very hurriedly built canoes the whole small sapling was used. The kind of sheathing employed in these canoes during the pre-Columbian era is a mystery. It would be quite unlikely that time was taken to split splints such as were used in the late elm-and spruce-bark canoes, when steel tools were available. The writers believe that for small canoes it may have been the practice to use a second sheet of stiff bark inside the first and extending only through the middle two-thirds of the length, across the bottom and up above the bilge but short of the gunwales. This, with the ribs and a few poles lashed to each rib along the bottom, would have given sufficient longitudinal strength and a stiff enough bottom for practical use. However, in large canoes of the type reputedly employed by Iroquois warriors, a stronger construction seems necessary, and these canoes may have had a number of split or whole poles lashed to the ribs along the bottom.