As the hollow gradually wore too large, a new one was made. The edges of the smaller cup-stones also frequently show evidence of their use in grinding down the surfaces of such stone implements. Such, however, is not the theory which finds favour in the Ohio Valley. There the hickory, or native walnut, abounds, with its hard shell, defying all ordinary efforts to reach the tempting kernel. But the boys have learned to hunt up a cupped stone, and placing the nut in its hollow, it is fractured at a blow with another stone, and its contents secured. Hence such objects are called nut-stones; and Mr. C. C. Jones, in his _Antiquities of the Southern Indians_, has adopted both the name and the idea implied in it, in spite of the occurrence of the same cups or depressions on rocks and boulders altogether inapplicable for such a purpose.[41] [Illustration: FIG. 21.—Cupped Boulder, Tronton, Ohio.] Whatever may have been the purpose of the cupped stones, they were not unknown to the ancient Mound-Builders. Messrs. Squier and Davis state that “in opening one of the mounds, a block of compact sandstone was discovered, in which were several circular depressions, in all respects resembling those in the work-blocks of coppersmiths, in which plates of metal are hammered to give them convexity.” These accordingly they suppose to have been the moulds in which the copper bosses and discs were formed, of which numerous examples have been obtained from the mounds. A highly characteristic example of what may not inaptly be styled a neolithic grindstone was found near Tronton, Ohio, in the summer of 1874. It is a large sandstone boulder, as shown in Fig. 21, covered with cups, or pits; and also, as will be seen, with long grooves, which suffice to prove its use as a stone for shaping and polishing tools. This adds confirmation to the probable origin of the cups from a like cause. Since I drew attention to the subject, I have been informed of the discovery of numerous similarly indented and grooved rocks along the shores of the Ohio river, including some of the hard granite, or Laurentian boulders. But gritty sandstone rocks appear to have been preferred.