The hollow was the result of receiving a blow, or the one of rotary frictions; the former showed that the stones were used for breaking the walnut shell and manufacturing stone tools while the latter indicated that pestles for making a fire were pressed down on the stone.
凹みは打撃を加えたものと回転摩擦痕跡によるものがあり、前者はクルミの殻割りや石器製作に使われたと考えられ、後者は火を起こすための火きり杵を上から押さえたものではないかと考えられている。