i62 REVIEWS 



required to secure satisfactory results. The reviewer is interested in 

 seeing what the writer will be able to do along similar lines with regard 

 to that anomaly in form-classification schemes, lake-shingle. It also 

 appears questionable whether, in view of the fact that protuberances 

 are more rapidly worn away in softer rocks, the scheme will not have to 

 be somewhat modified to fit smaller pebbles of softer material. 



This very point is, to some extent, met with in the second paper, 

 which is a concrete study of the ratios suggested and the distances 

 traveled by the pebbles. After locating a distinctive bed of quartzite 

 which outcropped in a stream vaUey, more than 600 pebbles from this 

 bed were collected at intervals downstream from the outcrop. Mileage 

 traveled was plotted against "roundness ratio" for each pebble. For 

 compiling these data the unknown hardness factor, which varied with 

 each pebble, had to be ignored. It was found, however, that the round- 

 ness ratio is proportional to the linear size of the pebbles. 



After the application of various corrections, the resulting curve was 

 compared with that obtained by "artificial erosion" of pebbles in a 

 motor-driven, water-filled, rotation barrel. It was found that the two 

 corresponded fairly closely. 



It seems, then, that the degree of rounding of pebbles may be accepted 

 as a fairly satisfactory means of estimating the distance which this 

 material has traveled. The careful writer points out several minor 

 vitiations of this principle and the reviewer recognizes that these are of 

 importance in the immediate and practical application of the methods 

 here outlined. But he holds that the general scheme outlined above 

 is the clue to much that is yet unsolved in the origin of certain conglom- 

 erates and erratics. The Geological Survey is to be commended for 



aiding such work as is presented in this paper. 



C. H. Behre, Jr. 

 Lehigh University 



An Introduction to the Geology of New South Wales. By C. A. 

 SussMiLCH, Third edition, revised and enlarged. Pp. 281, 

 figs. 92, tables 5, and folded geological map. Angus & Robert- 

 son, Sydney, 1922. 

 The third edition of this very excellent and useful work has now 

 appeared, eight years after the appearance of the second edition. The 

 principal changes will be found in the chapter on the Carboniferous 

 period, to which notable additions have been made. The Carboniferous 



