22 T. W. E. DAVID. 



and W., whereas westwards the folds bend somewhat to 

 W. of N. inclining eventually to W.N.W. As far as can be 

 judged from the sections supplied by these authors, there 

 is a slight overfolding from N. to S. 



As regards newer structure lines it seems probable from 

 the steepness of the southern escarpment of the Mac- 

 Donnells and its narrow rocky canons, such as those of 

 Redbank Gorge, and the gorge of the Finke River, that 

 there has been comparatively recent movement along an 

 old E. and W. fault plane. The most important of these 

 newer tectonic lines, as has been indicated by Mr. Howchin, 1 

 Prof. Gregory, 2 and Mr. W. N. Benson, b.sc., 3 are the series 

 of important and comparatively recent zones of fractures 

 which run more or less meridionally between the western 

 scarps of the Mount Lofty Ranges and the high western 

 plateau bouuding Lake Torrens on the west. In this 

 fractured and foundered area, termed by Professor Gregory 

 the 'Rift Valley of Australia,' lie St. Vincent and Spencer 

 Gulfs, Lake Torrens, Lake Eyre etc., the last mentioned at 

 its centre being about sixty feet below sea level. This 

 region appears to have been an area of subsidence from 

 very early time. Even the lower Cambrian strata of 

 Mount Lofty crept westwards in their effort to fill up this 

 senkungsfeld ; and in his latest paper Mr. Howchin has 

 shown that even the Miocene strata to the south of Adelaide 

 have been overfolded in the same direction. 



The earthquake which visited the Adelaide region on 

 September 19th, 1902, appears to have had its epicentre 

 near Warooka towards the southern end of Yorke Peninsula. 

 This proves that movement of the earth's crust along this 

 important zone is still in progress. The accompanying 



1 Q.J.G.S., Vol. lxiv, p. 234-263, pis. xxvi-xxix. Geography of S. 

 Australia, pp. 88, 89 and 100 ; and Trans. Roy. S. S.A., Vol. xxvin, 1904, 

 pp. 253 - 280, pis. xxxvii - xliv, and ibid. Vol. xxx, 106, pp. 227 - 262, pi. xi. 



2 Dead Heart of Australia. 



3 Trans. Roy, Soc. S.A., Vol. xxxin, 1909, pp. 106-7, and ibid. 1910. 



