Form with Transverse Ridge at Shoulder-line of Blade

This peculiar ridge across the shoulder-line or top of the blade is not often met with; but there are half a dozen good examples in the Museum. These have prominent ridges, but some other specimens show a small ridge less sharply defined, and this type merges into the common form, which merely has the shoulder, or junction of the blade-bevel on the back with the axial plane of the back, sharply defined as an angle of greater or less obtuseness, but on which no supplementary ridge or raised part is seen. The only reason for the existence of this peculiar transverse ridge on the back of an adze at the shoulder-line, as obtained from natives, is that it served to force the chip upward and detach it from the baulk being worked, and also to prevent the adze-blade from being bound in the cut. This, however, was merely a supposition. It is well known that the uma of a stone adze was carefully designed for that object.

It is curious that this transverse ridge is often accompanied by straight backs and a marked slope inwards of the sides, causing the back of the tool to be considerably narrower than the face. Thus, in page 302a specimen (fig. 88, Plate X) 8½ in. long, 2½ in. wide at the cutting-edge, and 1¾ in. near the poll, the face just behind the shoulder is 2⅝ in. wide, whereas the back is only 2 in. wide on the same section. Also, the back, from the poll to the rise of the transverse ridge, is perfectly straight and flat, not being at all convex either way, a very rare thing, save in very small forms. The sides also are almost straight, indeed very slightly concave longitudinally, and unusually flat transversely. The ridge across the shoulder-line is prominent, and comes to quite a sharp point on top. The thickness at the ridge is 1¼ in., and in the middle 1 in. The tool has been well ground except on the back, and is disfigured only by two gaps in the blade and one near the butt end. Well-defined striæ show that one side has been rubbed obliquely on the grinding-stone. On the other side both oblique and longitudinal striæ are visible. Material, black-veined aphanite. Angle of blade, 45° to 30°. Weight, 1 lb. 14 oz.

Another specimen is 7½ in. long, and has a somewhat thinner blade than the one last described. It is not, however, so symmetrical, a long flake having been struck off one side, apparently in the blocking-out process, which has produced a disfiguring hollow in that side. A longitudinal curve on the opposite side has possibly been formed in order to strengthen the weakened part of the tool. The transverse ridge will be noted in several types.