In the Thirteenth Annual Report of the Bureau of Ethnology, page 59, the following statement is to be found: " The obsidian flakes of the Aztecs resemble the flint flakes of our ancestors, not so much because the ancient Briton resembled the Aztec, as because the fracture of flint is like that of obsidian." The fracture of flint is like that of obsidian in that both break with what is called conchoidal fracture. But there are different degrees of conchoidal fracture, that of obsidian being

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... and possessing an accompaniment which that of flint does not have. The aim of this paper is to describe the distinguishing features of obsidian fracture, to seek an explanation for the same, and to show that to them is due, in a measure at least, the excellence of obsidian as a material for knife-and razor-making. To compare flakes and nuclei or cores only, the curves in obsidian are more delicate and graceful than those in flint. Flints differ in quality among themselves; so do obsidians, depending especially upon their homogeneity. There seems to be a stiffness in the flint flake; it resembles the arc of a more or less rude circle. On the other hand, the curve in the obsidian flake (figure 49), beginning with the percussion end or base, is first sharp, then, for the greater part of its course, very gentle indeed, and lastly, sharp again-somewhat sharper than the initial one. Corresponding phenomena are observed in the cores. In addition, the obsidian fracture possesses a feature not found in that of flint. If the edges of an obsidian flake on its nuclear or inner surface be examined carefully with a pocket lens, or even with the naked eye, several series of parallel lines or markings of varying length and remarkable for their regularity are easily AM. ANTH. N. S., 2-27 417 418 AMERICAN ANTHROPOLOGIST [N. S., 2, 19O