16 T. W. B. DAVID. 



In his introduction to Mr. Howchin's Geography of South 

 Australia, Professor Gregory contends that (op. cit., p. 25 

 26, fig. 6) there is evidence of two distinct groups of folds 

 in South Australia, differing in date of birth as well as in 

 direction. The older group has dominant E. and W. trends, 

 the newer according to Gregory, have a nearly meridional 

 trend inclining slightly to W. of N. His conclusions are 

 evidently based on the observations of Mr. Howchin (op. 

 eit., pp. 77 — 92). This very important problem will be 

 discussed presently. 



Reference to the relief map, re South Australia, makes it 

 clear that the most conspicuous tectonic feature is that of 

 the depressed area in which lie Lakes Eyre and Torrens 

 prolonged southwards into the subsidence regions of 

 Spencer's Gulf and St. Vincent's Gulf, and bounded east- 

 wards by the western escarpment of the Mount Lofty and 

 Flinders Ranges. Westwards the depressed area is bounded 

 by the eastern edge of the great plateau of Central Aus- 

 tralia near the west shores of Lake Torrens. If we refer 

 to the map on Plate 2, commencing at Kangaroo Island 

 and trace the lines of fold northwards, we cannot fail to be 

 struck with the evidence of either a gradual change in the 

 trend of the fold lines, or of the existence of two different 

 groups of folds as argued by Mr. Howchin and Professor 

 Gregory. The geological map is strongly in favour of a 

 virgation and general meeting of the trend lines in syntactic 

 arcs from Kangaroo Island to the Mount Lofty Ranges, 

 and from the Mount Lofty Ranges to the Barrier Ranges. 

 Dr. Woolnough in the paper just quoted, argues that the 

 crystalline rocks on the eastern side of the Mount Lofty 

 Ranges represent folded Pre-Cambrian rocks, the trend of 

 whose folds agrees approximately with the later folds of 

 the Cambrian strata. Mr. Howchin on the other hand 

 holds that these crystalline rocks of the eastern Mount 



