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NOTES ON'THE GEOLOGICAL FEATURES OF THE MEADOWS VALLEY. 



By D. Mawson, Kt., D.Sc, F.R.S. 

 [Read October 11, 1923.] 



Physiography. 



Two valuable papers ^^^ have been written on the Geology and Physiography 

 of the Meadows Valley by Dr. E. O. Teale. 



The present contribution supplies some additional facts, more particularly 

 relating to the vicinity of Blackfellow's Creek, which, though not a confluent of 

 the Meadows Creek itself, is nevertheless embraced within the major boundaries 

 of the Meadows Valley, namely, the Willunga Range and the Mount Magnificent 

 Range. These latter ridges are remarkably accordant in height and are remnants 

 of a former peneplanation. Between them is a broad shallow valley from five 

 to six miles wide, with a floor at a level of about 1,000 feet above the sea and 

 some 300 feet below the summit line of the ridges on either side. 



Towards its northern end, between Wickham's Hill and Prospect Hill, is 

 an unbroken depression. Here the rocks on either flank are steeply dipping 

 quartzite and slaty beds of the Adelaide Series, whilst the central area is deeply 

 silted up with horizontally bedded clayey and sandy strata of a more recent age. 



Southward of this location, a central elevated block of "Barossian" gneissic 

 rocks occupies much of the region between the limiting ranges. This block of 

 ancient crystalline rocks is being dissected by three streams, all of which, to the 

 south, enter the region of Permo-Carboniferous glacial sedimentation already 

 described by Professor W. Howchin.*^-) On its western margin is the Myponga 

 Creek heading up from the south. On its eastern side Blackfellow's Creek is 

 cutting its way along the junction of the "Barossian" and "Adelaide Series," also 

 heading to the north. Both of these streams are of consequent type. The 

 Meadows Creek itself flows southward over the soft sedimentary accumulation 

 of the valley floor until meeting the "Barossian" rocks, through the tough body 

 of which it flows without deflection. Thus the Meadows Creek occupies an 

 inherited course. The toughness of the crystalline complex to the south limits 

 the rate of downward erosion, which has resulted in the preservation of so much 

 of the soft valley filling as still remains in its upper course. Had the flow of 

 the Meadows Creek followed strictly consequent lines it would have been con- 

 tinuous with the Myponga Creek. 



Dr. Teale reports "^^^ having found a glaciated boulder in a road cutting near 

 Dingabledinga School, which is towards the, southern end of the Meadows Valley. 

 That discovery led him to suggest that possibly "the Meadows Valley may, in 

 part, be a trough, the earliest features of which are due to glacial erosion in 

 Permo-Carboniferous times." 



As a result of numerous visits to that locality before Dr. Teale's paper was 

 published, I had begun to suspect that the physiography was likely to be partly 

 Permo-Carboniferous glacial, and the news of the discovery by Dr. Teale of an 

 ice-scratched boulder did not come as a great surprise. Since then my atten- 

 tion has been directed by Mr. W. Durward, Chief Forester of the Government 



(1) "The Physiography of the Meadows Valley," Trans. Roy. Soc. S. Austr., xlvi., 1922, 

 p. 160. "Soil Survey and Forest Physiography of Kuitpo," Bulletin No. 6, Dept. of Forestry, 

 University of Adelaide. 



(2) "Description of a new and extensive area of Permo-Carboniferous Glacial Deposits 

 in South Australia," Trans. Roy. Soc. S. Austr., xxxiv., 1910, p. 231. 



(3) Trans. Roy. Soc. S. Austr., xlvi., 1922, p. 163. 



