STONE IMPLEMENTS FROM SHORES OP LAKE MICHIGAN. 593 



are directed obliquely to the plane of the edge the modification is gen- 

 erally in that part of tlie circumference uear the percussion notch, 

 where the edge is like that of a half sphere. The oblique striae run 

 into the rough surface of the flake, as shown in Plate III, fig. 7. 



Of the 228 specimens studied, 166 have the edge altered by chipping 

 incident to use. Few or many chips have been broken from the edge, 

 and commonly from what was its sharpest portion. Besides the chip- 

 ping, an added loss is seen, in such cases, in the rounding off and often 

 in the polishing of angles or prominences of the edge, whether of the 

 original flake or where it has been altered by the chipping. In some 

 specimens the facets left by chipping are of different ages; some are 

 little worn where they meet the edge of the flake, while others are 

 almost obliterated. Chipping of the edge is apt to be most marked in 

 heavy flakes, and especially in those having well-developed marks of 

 use. Occasionally the chipping has worked a notch in the edge to 

 which most of the wear is limited. Where the chipping is greatly 

 developed the edge is roughly blunted, presenting a battered appear- 

 ance. The chipping here referred to is the result of use. and is not 

 designed. 



The simple rounded, often polished edge, is present in some part of 

 the circumference of 211 out of the 228 specimens examined. The 

 rounding is often the only modification of the edge. (Plate III, fig. 6.) 

 The abrasion in cases extends over chipped portions and irregularities. 



Modifications of the face of fracture in the nature of smoothly worn 

 and striated portions, distinct from changes incident to wear at the 

 edge, occur in 87 flakes. (Plate III, figs. 3 and 4.) These vary from a 

 slight reduction of the roughness of the stone to a marked grinding of 

 the whole surface. The middle of the face is always more worn than 

 parts nearer the circumference. Striae are usually short, but some 

 extend nearly the length of the flake and cross others at various 

 angles. Sometimes a groove is worn in the face of the stone correspond- 

 ing in direction with the greater number of scratches. All save 9 of 

 the 87 specimens show striation. In these 9 only the more prominent 

 irregularities have been touched by the grinding. In a few cases the 

 striae are arranged in broken circles around the center of the flake and 

 more or less concentric, indicating a circular movement of the stone 

 in use. 



The changes thus described are readily distinguished from changes 

 produced by natural agencies, chemical or mechanical. Wear produced 

 by water and ice action is of a totally distinct nature, and alterations 

 of the surface by decay operate alike on all surfaces, giving no hint of 

 the specialization which comes about through use. 



Uses illustrated. — The trap flake was used in various ways, some of 

 which are»illustrated in Plate V. As a scraper, «,, it was held perpen- 

 dicularly to the surface operated upon, or approximately so, and moved 

 in the direction indicated by tlie arrow; with downward pressure the 

 SM 97 38 



