J 14 J. T. JiUson ; Drift of Rock Debris. 



The suggested explanation has objections to it. A number of 

 loose stones of various sizes and shapes would apparently move 

 forward, even under the special conditions of furrowing postu- 

 lated, at very different times, and thus the parallelism of the lines 

 would be destroyed; and before it was regained, practically the 

 whole of the stones on the " ridge " would have to fall into the 

 furrow. This could possibly, and perhaps does, as suggested 

 .above, occur, since the stones remaining on the ridge would con- 

 tinue to be undermined, whilst those reaching the furrow would 

 •escape this process for the time being. Such a peculiar combina- 

 tion of conditions may occasionally result, but it could hardly 

 be expected to "be widespread, and apparently it is not. The 

 matter is brought forward so that further instances in Western 

 Australia or elsewhere might be searched for and studied in the 

 field. So far as the writer is aware, no other example of gravi- 

 tational drift of rock debris in parallel lines has been recorded. 



Tolman 5 has emphasized the importance of a " desert pave- 

 ment " as a protection of the underlying rocks against erosion. 

 Such pavements of -quartz occur at Goongarrie, and will be 

 •described in another paper. The present paper, however, shows 

 that where the pavement is not complete, although there is a 

 measure of protection, yet considerable erosion may take place. 

 It may be remarked in this connection that S. Goczel 6 had as 

 early as 1894 pointed out that the pebble-covered areas were a 

 protection against wind erosion of the underlying material. 



DESCRIPTION OF PLATE V., Figure 3. 



Pig. 3. — The white quartz debris is derived from the reef in 

 the background. Bands of black shales are shown 

 alternating with parallel bands of quartz debris, espec- 

 ially in the foreground. The bands are parallel to the 

 strike of the shales. 

 Floor of Lake Goongarrie. 



5. Tolman C. F. — " Erosion and Deposition in the Southern Arizona 

 Bolson Region." Journ. Geol., 1909, Vol. XVII.. p. 149. 



6. Goczel, S. — " Report on the Central Goldfields of Western Australia," 

 Appendix V., pp. 24-33. Ad Interim Report of the Department of Mines 

 for half-year ending 30th June, 1894. 



