[Pboc. Roy. Soc. Victoria, 33 (N.S.), 1921] 



Akt. VII. — Note on the "Dimpling" of Granite Hills in 

 Sab- A rid Western Australia. 



By J. T. JUTSON. 



(With Plate V., Figures 1, 2.) 

 TRead 12th August, 1920.] 



In the south-central sub-arid portion of Western Australia, a 

 large number of low and comparatively small isolated hills of 

 granite rise above the surrounding elevated plain or plateau, 

 which forms so marked a feature in Western Australian physio- 

 graphy. These hills are usually almost, if not entirely, destitute 

 of vegetation and of soil, and they are like minute scattered 

 islands rising from the sea of ordinary vegetation-bearing coun- 

 try. They have played an important part in the exploration and 

 opening-up of the interior of Western Australia ; for it is at their 

 feet, or on their sides that " soaks " or rock holes, carrying water, 

 may be found. It is on such supplies that the aborigines largely 

 depended, and they were a most valuable aid to the white man in 

 penetrating to the arid interior of the continent. 



These hills show the usual rounded flowing surface — due to 

 spheroidal weathering — common to granite in many parts of the 

 world; and also the boulders that result from such weathering. 

 They, however, differ from the moister areas in the peculiar 

 ^undermining and hollowing out from below upwards of many of 

 :the boulders, the result of which processes is to be seen in the 

 grotesque forms often assumed by the granite. 



In addition to these features, several hills that the writer 

 has seen — and doubtless what is to be described is a common 

 phenomenon — show, when examined in detail, a peculiarly ir- 

 regular, although still rounded, outline. This feature is due to 

 the occurrence of a number of shallow cavities or holes, and the 

 general effect is a dimpled appearance of the surface. Hence 

 the term " dimpling " may be used to indicate the process by 

 which such cavities are formed. The " dimples " are circular, 

 •elliptical or oval in outline, are from two to three feet to ten 

 feet or more in their longer diameters, and are from a few inches 

 to three or four feet deep at their deepest part. Their walls 



