THE DARLING PENEPLAIN OF WESTERN AUSTRALIA. 393 
tion of the climate prevented the development of young 
consequent streams on the eastern side of the peneplain, 
and the previous normal erosion gave place to the cycle of 
arid erosion through which the region is passing at present. 
The author is of opinion that such a mode of development 
reconciles the somewhat divergent views which have sought 
to explain the great salt lake systems by arid erosion, by 
river erosion or by wave action.’ 
The author has not travelled sufficiently extensively in 
the salt lake region to be able to speak with the same cer- 
tainty as with respect to the Darling Range area, but 
wishes to suggest that some of the higher hillsin that area 
such as Mount Burgess, north of Coolgardie, may possibly 
be residuals of the Mount Dale level. It is possible also _ 
that the recognition of a mature valley cycle of erosion 
may assist in explaining some of the difficulties which exist 
in connection with the origin of the deep leads of Norseman 
and elsewhere. Jutson has explicitly assumed such a cycle, 
subsequent to the main planation of the area (loc. cit., p.98). 
Age of the Different Levels. 
The author agrees in every point with Jutson as to the 
evidences of date of peneplanation afforded by the Irwin 
River sections and those from that point southward to 
Gingin. .The author has had an opportunity recently of 
re-examining the Irwin River area, and is convinced not 
only that: ‘“‘the Jurassic rocks in the Irwin River district 
were uplifted with the granite,’”’ (Jutson, p. 94), but that 
the laterite level marking the Darling peneplain is con- 
tinuous across the old fault plane which marks their junc- 
* Gregory, J. W., “ The central lakes of Westralia and the Westralian 
peneplain,” Geog. Journ. 1916, pp. 326—331. Jutson, J. T., “Erosion and 
the resulting land forms in sub-arid Western Australia, including the 
origin and growth of the dry lakes,’ Geog. Journ., 1917, pp. 418-437. 
Montgomery, A., “The significance of some physiographic characteristics 
of Western Australia,” Journ. Roy. Soc. W.A., vol. 11, 1915-6, pp. 59— 96. 
