“After expressing himself in this manner he went on to explain what he had seen. He considered making flakes much more of an art than the shaping them into arrow- or spear-points, for a thorough knowledge of the nature of the stone to be flaked was essential, as a slight difference in its quality necessitated a totally different mode of treatment. The principal source of supply for what he termed home-made flakes was the coarse gravel bars of the rivers, where large pebbles are found; those most easily worked into flakes for small arrow-points were chalcedony, jasper, and agate. Most of the tribes had men who were expert at flaking, and who could decide at sight the best mode of working. Some of these pebbles would split into tolerably good flakes by quick and sharp blows striking on the same point; others would break by a cross-fracture into two or more pieces; these were preferred, as good flakes could be split from their clean fractured surface by what Mr. Catlin called impulsive pressure, the tool used being a shaft or stick of between two and three inches diameter, varying in length from thirty inches to four feet, according to the manner of using them. These shafts were pointed with bone or buck-horn, inserted in the working end bound with sinews, or rawhide thongs, to prevent splitting. (See Fig. 15.) For some kinds of work the bone or horn tips were scraped to a rather blunt point, others with a slightly rounded end of about one half inch in diameter. He described various ways of holding the stone while the pressure was being applied. A water-worn pebble broken transversely was commonly held by being sufficiently embedded in hard earth to prevent its slipping when held by the foot as the pressure was applied. Large blocks of obsidian or any easily flaked stones were held between the feet of the operator while sitting on the ground, the impulsive pressure being given to the tool grasped in both hands, a cross-piece on the upper end resting against his chest, the bone end against the stone in a slight indentation, previously prepared, to give the proper angle and to prevent slipping.