A LABORATORY AND FIELD STUDY OF 

 COBBLE ABRASION 



Preliminary Report 



CHESTER K. WENTWORTH 



University of Chicago 



INTRODUCTION AND OBJECT 



In the course of field work at Baraboo, Wisconsin, in the summer 

 of 19 1 6, it occurred to me that by means of a suitably designed 

 tumbling barrel an experimental study might be made of the abra- 

 sion 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 191 7, 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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