598 president's address. 



Ranges, the Archaean sediments were strongly folded. The axes 

 of the fohls in North Western Tasmania strike N. 25° W. towards 

 the Western portion of Victoria, and trending towards Leigh's 

 Creek, in South Australia, where north-westerly axes of folds are 

 strongly developed in the Cambrian rocks. A short distance 

 S.W. of Silverton these north-westerly axes of folding meet 

 almost at right angles a strong N.E. and S.W. axis, the Adelaide 

 Axis, which runs from Yorke's Peninsula to beyond Silverton. 

 Following the north-westerly axis, which may be termed the 

 Tasmanian Axis, towards the Musgrave and Macdonnell Ranges, 

 the strike changes to due E. and W. There is evidence there too, 

 as at Yorke's Peninsula, to show that the folding of the Archsean 

 rocks was Pre-Cambrian, as there is an unconformability between 

 the Archaean group and the Cambrian system. From the west 

 end of the Macdonnell Ranges, it would seem that the Archaean 

 folds swing once more back on to their former bearing ; as in the 

 Kimberley District there are strong N.W. and S.E. folds in the 

 Archaean group, with, however, a N.E. axis crossing it and strik- 

 ing towards the Ord River. No conclusive evidence has been 

 obtained to show when this folding took place at Kimberley, but 

 it was probably chiefly Pre-Cambrian. In Tasmania the general 

 evidence shows that the folding of the Archaean was earlier, at all 

 events, than Upper Cambrian, as the Caroline Creek beds, of the 

 latter age, are considered unconformable to the Archaean group. 



The general features of the axis of folding in Archaean time in 

 Australasia appear to be as follows : — A long shallow loop, like 

 a railway curve, commencing in Tasmania and trending thence to 

 the Macdonnell and Musgrave Ranges, the convexity of the 

 curve facing N.E., then a reverse curve from the Macdonnell 

 Ranges to Kimberley. To the S.W. of Silverton, this doubly 

 curved Tasmanian Axis is crossed by the Adelaide Axis from S.W. 

 to N.E. 



This powerful folding in Pre-Cambrian time, considered in 

 conjunction with the fact that in the Pre-Cambrian as well 

 as in the succeeding Cambrian System there are conglomerates 

 and ripple marks (?) indicative of shallow water conditions, 



