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In the course of field work at Baraboo, Wisconsin, in the summer of 1916, it occurred to me that by means of a suitably designed tumbling barrel an experimental study might be made of the abrasion of cobbles in stream transit. It was believed that by carefully controlling conditions, quantitative determination of change of shape and size as related to distance of travel could be made which, when later combined with field studies, would serve as a valuable criterion in the study of deposits of transported materials. Later in in the summer of 1917, during occasional examinations of gravel deposits, the idea was so cordially received by Mr. A. J. Collier, of the U.S. Geological Survey, that I undertook the study of cobble abrasion at the University of Chicago the following autumn and have continued it, with some interruptions, to the spring of 1919. The following is a brief statement of the principal phases of the problem, the methods used, the more significant results obtained to date, and the points which I hope to take up in the future. More complete description of the methods and more thorough discussion of various conditions and their significance will be reserved for a later paper. OUTLINE OF STUDY Aside from lithologic character, the distinguishing features of any cobble are its size, shape, and surface texture. These are subject to change and the change is frequently characteristic of the transporting agent. In stream transportation the rate of change in size of a given piece depends on: (i) its own size; (2) the size of associated cobbles;
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