. Bulletin. Science; Natural history; Natural history. Fig. 7. Anomalous cobble modifications. Fragments d, e, g, i, 1, and m are spalled off pieces of cobbles found in Indian middens on Santa Catalina Island. These were used as choppers, scrapers, gravers, etc. (Santa Catalina Island Museum Anthropological Collection). Spalls c and h are from Salta Verde Point terrace (TS-7) and j is a quartzite spall from Ripper's Cove, a' is a spall chipped by the authors from a prolate cobble from the Salta Verde Site (TS-7). The spalls illustrated are com- posed of dacite porphyry and quartzite. classific
. Bulletin. Science; Natural history; Natural history. Fig. 7. Anomalous cobble modifications. Fragments d, e, g, i, 1, and m are spalled off pieces of cobbles found in Indian middens on Santa Catalina Island. These were used as choppers, scrapers, gravers, etc. (Santa Catalina Island Museum Anthropological Collection). Spalls c and h are from Salta Verde Point terrace (TS-7) and j is a quartzite spall from Ripper's Cove, a' is a spall chipped by the authors from a prolate cobble from the Salta Verde Site (TS-7). The spalls illustrated are com- posed of dacite porphyry and quartzite. classifications, especially 128-256 mm, produced characteristically low i//p. These low mean sphericity values are indicative of wave formed rocks. This apparent bimodal condition had been found on high wave energy, gravel beaches by Dod- kins and Folk (1970). Under these conditions there is a tendency for smaller pebbles to be tossed about randomly, to be abraded more uniformly and to fall into the interstitial spaces between larger rocks where they are rolled back and forth by wave action rather than slide. In the case of sandy beaches, it was found that pebbles of all sizes have uniformly low sphericities. This condition of wave force discrimination in pebble shaping, producing wide range of Maximum Projection Sphericities, is evident in all of the sites sampled. We conclude, therefore, that similar physical conditions existed during the Qua- ternary period for at least 3 of the 4 sites sampled (sites TS-4, TS-5, and TS-6), and, in all probability, for the TS-7 site. The Cottonwood Canyon Beach control site is typical of the aforementioned physical parameters to pebble type devel- opment, namely, high wave energy (waves averaging over m in height) and a gravel beach. These parameters have produced a low mean Maximum Projec- tion Sphericity for the site of , giving it at least a 959f certainty that the pebbles are wave Please note that these images are extracted from
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