One day Ab went into Old Mok's cave grumbling. "I shot an arrow into a great deer," he said, "and I was close and shot it with all my force, but the beast ran before it fell and we had far to carry the meat. I tore the arrow from him and the blood upon the shaft showed that it had not gone half way in. I looked at the arrow and there was a jagged point uprising from its side. How can a man drive deeply an arrow which is so rough? Are you getting too old to make good spears and arrows, Mok?" And the man fumed a little. Old Mok made no reply, but he thought long and deeply after Ab had left the cave. Certainly Ab must have good arrows! Was there any way of bettering them? And, the next day, the crippled old man might have been seen looking for something beside the creek where it found its exit from the valley. There were stones ground into smoothness tossed up along the shore and the old man studied them most carefully. Many times he had bent over a stream, watching, thinking, but this time he acted. He noted a small sandstone block against which were rasping stones of harder texture, and he picked this from the tumbling current and carried it to his cave. Then, pouring a little water upon a depression in the stone's face, he selected his best big arrowhead and began rubbing it upon the wet sandstone. It was a weary work, for flint and sandstone are different things and flint is much the harder, but there came a slow result. Smoother and smoother became the chipped arrowhead, and two days later--for all the waking hours of two days were required in the weary grinding--Old Mok gave to Ab an arrow as smooth of surface and keen of edge as ever flew from bow while stone was used. And not many years passed--as years are counted in old history--before the smoothed stone weaponhead became the common property of cave men. The time of chipped stone had ended and that of smoothed stone had begun. There was no space between them to be counted now. One swiftly became the other. It was a matter of necessity, this exhibition of enterprise and sense by the early man in the prompt general utilization of a new discovery. And not alone in the improvements in means which came when men of the hunting type were so gathered in a community were the bow and the smoothed implements, though these were the greatest of the discoveries of the epoch. The fishermen who went to the river were not content with the raft-like devices of the aquatic Shell People and learned, in time, that hollowed logs would float and that, with the aid of fire and flint axes, a great log could be hollowed. And never a Phoenician ship-builder, never a Fulton of the steamer, never a modern designer of great yachts, stood higher in the estimation of his fellows than stood the expert in the making of the rude boats, as uncouth in appearance as the river-horse which sometimes upset them, but from which men could, at least, let down their lines or dart their spears to secure the fish in the teeming