43 ± J. T. Jut son — Rounding of Pebbles. 



ments of the water channels are being moved fairly fast 

 down stream by the intermittent stream action, and that 

 this movement prevents the rain from beating long 

 enough on one particular surface to bring, about the 

 rounding; 6 and also that when rain falls the channels 

 must at times receive sufficient water to cover the debris 

 on their floors, and thus prevent further direct falls of 

 rain on to the rock fragments. Be this as it may, the 

 explanation given for the rounded pebbles of the hill- 

 sides, and at their bases on lake shores, appears to be 

 the only feasible one. It at least appears certain that 

 they are being rounded in their present positions, and 

 that they are not due to past normal stream, lake, or 

 marine action. 



The Bearing of the Origin of the Pebbles on Certain 



Questions. 



A true conception of the origin of the rounded pebbles 

 is required in view of the incorrect inferences that may 

 be drawn from their occurrence, if such pebbles are 

 assumed to be due to either stream, lake, or marine ac- 

 tion; such inferences must be that large rivers or lakes 

 (probably freshwater) earlier existed in the area; or 

 that the land has been recently subjected to marine ero- 

 sion. The nature of the pebbles does not support any 

 of these deductions. 



H. E. Gregory has shown that, under certain condi- 

 tions, pebbles may be carried considerable distances by 

 streams and yet remain angular or sub-angular, 7 and 

 that ancient river gravels may not in all cases be dis- 

 tinguishable from residual deposits resulting directly 

 from weathering. 8 



In the area of which this paper treats, these statements 

 are confirmed to the extent that the true stream-borne 

 pebbles are angular and sub-angular, while the rounded 

 pebbles have received their present shapes in practically 

 their present positions, which are close to the parent 

 rocks. The angular character of the stream-borne peb- 

 bles may however, be entirely due to the short distance 

 they have travelled. 



Perth, Western Australia. 



6 The absence of rounding in these stream fragments would also seem 

 to imply that flaking is not a very potent agent in the formation of the 

 greenstone pebbles described in this paper. 



7 Op. cit. p. 302. 



8 Op. cit. p. 303. 



