A STUDY OF COBBLE ABRASION 521 



It is hoped that by a study of the crescentic impact scars on 

 some compact quartzites and other rocks an approximate quanti- 

 tative measure may be made of conditions under which a given 

 deposit was transported and its history thereby interpreted, but 

 no detailed study has been made. 



CONCLUSION 



Experimental studies, physical or chemical, are of little value to 

 the geologist until they have been applied to actual field conditions. 

 In the studies described and planned above I have tried to keep in 

 mind the possible field appHcations and hope, as time permits, to 

 point out by field studies the value of each one of the foregoing 

 relations in throwing further fight on the past history of the earth. 

 I am especially desirous of receiving opinions on the method of 

 measuring and defining roundness described and used in (17) 

 above, and will appreciate criticism and comment on any other 

 points which have been overlooked or are subject to different 

 interpretation. 



