52 T. W. E. DAVID. 



Pre-Cambrian. — In Pre-Oambrian time the rocks of that 

 age in West Australia were folded in the form of an open 

 inverted S, thus Q. In South Australia from Kangaroo 

 Island to Broken Hill the Pre-Oambrian rocks are folded on 

 the pattern of a normal but very open S- At the southern 

 part the overthrusting is to the N.W. and W., in the northern 

 to the S.E. and E. Still further north virgation takes 

 place. In central Australia, at the Musgrave and Mac- 

 Donnel Ranges, the folding is nearly E. and W. with a 

 tendency in the Musgrave to overfold northwards, and in 

 the MacDonnel Range southwards. In West Australia the 

 direction of folding in the southern pari of the reversed S 

 is towards the W. and W.S.W., and in the northern portion 

 partly to the N.E., partly to S.W. 



In Tasmania N.N.W. trends predominate, and there 

 appears to be a virgation of the folds, from between N.N.W. 

 to a little E. of N., but this does not become strongly 

 accentuated until Post-Silurian time. The Tasman folds 

 thus form a V. In the Northern Territory the folds run a 

 little W. of N. and E. of S. In the Kimberley District of 

 West Australia they form an arc, the convexity of which 

 is directed southwards. 



The Cambro-Ordovician rocks are strongly unconform- 

 able to the Pre-Cambrian, but in Tasmania and Victoria 

 they appear to have been folded sympathetically with the 

 latter. In the Mount Lofty and Yorke Peninsula areas of 

 South Australia the folds of Cambrian and Pre-Oambrian 

 rocks closely agree, but to the N. of Lake Torrens and S.W. 

 of Lake Eyre there is considerable divergence between the 

 Cambrian and Pre-Cambrian trends, the former inclining 

 to meridional, and the latter to nearly E. and W. lines. 

 The Cambrian Divide lay S. or S.E. of Adelaide in the direc- 

 tion of Jeffreys Deep, the quarter from which moved the 

 ice which produced the vast boulder clays and erratics of 



