THE DARLING PENEPLAIN OF WESTERN AUSTRALIA. 391 
*“subsequent’’ streams, some of which probably fell south- 
wards while others flowed tothe north. Asaresult of the 
production of the Darling Scarp, new, active, consequent 
rivers came into existence. Inthe area under review these 
streams flowed from east to west, and, rapidly extending 
their valleys headwards, they gradually dismembered the 
older streams and produced the present arrangement of the 
drainage. While this latter part of the question is treated 
by Jutson, the author differs from him in some of his con- 
clusions as to matters of detail, and intends to deal with 
the matter of river development in a subsequent paper. 
At Northam and York (Figs. 59 and 60, Jutson loc. cit.) 
the Avon River has not yet been affected by the piracy 
carried out by the Swan. The stream occupies its ancient 
mature valley. A little further north, at Toodyay, how- 
ever, the Swan is actively incising its valley and is ina 
comparatively youthful stage of development. Its bed lies 
far below the original valley bottom, but the positions of 
both the Darling Peneplain and of the Meckering Level can 
be traced quite readily; the former in the level-topped 
laterite covered hills of the 1,000 foot level, and the latter 
in the broad, gently sweeping, curved shoulders of these 
hills (Plate XXX, fig. 2). 
In many parts of the Darling Range there is a strong 
suggestion of two mature-valley levels, but much more 
investigation will be necessary before such a fact can be 
substantiated. Passing eastward across the mature valleys 
of the Avon, Logan and other streams, the clearness of 
definition of the Meckering Level is lost, though, all the 
way, to Southern Cross at all events, the existence of 
mature valleys is noticeable. This is only what would be 
expected on the theory ofa slight uplift after perfect pene- 
planation. The roughening of the land surface would be 
most pronounced near the coast, and would become less 
