“A heavy wagon, loaded with hogsheads of tobacco, drawn by five or six yoke of oxen, passed over the fresh-spread gravel with a sharp, crushing, grinding sound. On examining the wheel tracks I was surprised to find the slight impression the iron tire had made on the surface stones. They had been pressed aside from the wheels, leaving a slight rut, those under the wheels compressed together, but very little broken; not sufficient to account for the sharp, crackling noise made as the wagon wheels passed over them. On examining the effect from the tread of the wheels to the old road-bed, a depth of about six inches, I found most of the larger gravel stones under the top layer split, some into flakes, the fractures in various directions, some crossing others. This spread from the width of the wheel-tires to about three times as wide on the old road-bed. Many of the fresh fractures presented the forms and appearance of genuine cores, and would be mistaken for the work of man. It was a beautiful illustration of the effect of pressure on small points of contact. Our lady friends, often inveterate iced-tea drinkers, when they find a lump of ice too large for their glass, will, with a common toilet-pin between thumb and finger, press its point into the ice, tap its head with the handle of a case-knife, or give it a click with a thimble. The cohesion is destroyed and the ice splits with just such a fracture as is made by impulsive point pressure on the more tenacious and refractory chert. “These Paducah observations led to considerable investigation as to the action of lodged drift-logs on gravel bars, and finally to an experiment that I should recommend the Smithsonian Institution to try on more extensive scale than I was able to. “I filled a metal cylinder with pebbles of various sizes and shapes, brought a pressure by a screw on them through a plunger; immediately a crepitating sound was heard, which as the pressure increased became sharper and louder, at times almost explosive, as the interstices became filled with broken fragments, producing side pressure and cross fractures. The sound became more confused and died away. On emptying the cylinder, the result was many representations of the rude implements found in the drift.” So much for Sellars’s observations. I consider them remarkable. * * * * * A series of papers entitled, “Arrows and Arrow-makers,” appeared in the _American Anthropologist_, vol. IV, 1891. Professor Holmes’s paper (p. 49) particularly refers to the manufacture of arrow-points, although Drs. Wilson, Hoffman, and Hough, Captain Bourke, Professor Mason, and Mr. Flint contributed papers relating to various phases of the arrow and its use. [Illustration: FIG. 57. (S. 1–3.) Long, slender lance-heads. Material: fine yellow chert. H. M. Braun’s collection, East St. Louis, Illinois. ]