312 J. T. Jutson — Interpretation of the Dry Lakes 



towards the South Australian border. Again, no evidence of this 

 has been adduced. 



Erosion by terrestrial waters, either by river or lake, seems also 

 inadequate to explain the facts. Fluviatile action cannot be con- 

 ceived to produce such forms in their present positions. Former 

 deep permanent lakes could produce cliffs, but such cliffs would not 

 be restricted to practically one side only, nor, stating the matter in 

 another way, would the high belts of country be bounded by lakes, 

 and the rock-cliffs of such lakes, on mostly one side only. Further- 

 more, there is at present no evidence available that such deep 

 permanent lakes ever existed. Lacustrine deposits, with abundant 

 fossils, should occur, but so far they have not been discovered, apart 

 from the leaves in a deep alluvial deposit at Coolgardie. Rock 

 benches are characteristic marks of former deep permanent lakes, but 

 none has ever been found. ^ "With regard to the action of the present 

 lake waters, as they remain for such a short period and, so far as 

 observed by the writer, are only a few inches deep at the margin, 

 abrasion by such waters seem out of the question, although there is 

 probably some removal of fine detritus from the base of the cliffs by 

 the lapping of the transient waters. Moreover, the objection as to 

 abrasion on practically one side only, also applies to the present lake 

 waters. 



There remains, then, but wind erosion, and this most satisfactorily 

 explains the facts as at present known. It is not claimed that wind 

 erosion alone is competent to produce the cliffs and rock-floors, and 

 to cause the lakes to migrate. The subaerial agents of erosion, 

 comprising insolation, " exsudation," the beating action of rain, and 

 general atmospheric weathering, are wearing down the cliffs and 

 rock-floors, and the gentle lapping of the lake waters may remove 

 some of the detritus. The wind, however, seems to be the 

 dominating agent, partly by corrasion, but chiefly by deflation.' 

 The debris is swept away from the cliffs, thus allowing their further 

 destruction, and the billiard-table floors are produced. Sand is 

 carried around or across the lake by the wind and deposited on the 

 eastern and other sides. This, aided by the deposition of fine silt 

 on the lake floor, forces the water westward, thus assisting to bring 

 about its migration. In the course of such migration higher rock 

 belts are met, cliffs formed, and then gradually Avorn back. Hence 

 rock-cliffs and rock-floors occur on the western sides, and sands on 

 the eastern. 



If migration has occurred to any extent, and if such migration is 

 chiefly due to wind erosion, then, without regard to other consider- 

 ations, the lakes are undoubtedly, in part at least, deflation lakes. 



^ It is not contended that larger lakes never existed. They have possibly 

 done so, but there is no available evidence that they formed deep permanent 

 lakes. What evidence there is points, in some instances, to wider areas of 

 shallow ephemeral lakes or playas practically similar to those now in existence, 

 and to the probability that such greater lakes have, owing to local conditions, 

 shrunk. In other instances the migration of a lake may account for an 

 apparently greater former lake of the playa type. 



