249 



are best understood by applying to them the theory of a 

 trough fault. 



IX.— Basal Beds of the Cambrian Series (Basal Grits 

 and Conglomerates). 



For some time my attention has been directed to a series 

 of outcrops which exhibit features no less interesting than 

 difficult of interpretation. In general aspect they vary from 

 fine-grained, white, felspathic sandstones and grits, through 

 every gradation of coarseness to pebbly conglomerates. The 

 lithological features were strongly suggestive of their being 

 basal beds resting on an older and unconformable series. 

 This first impression as to their origin has been gradually 

 strengthened with more extended acquaintance, and there is 

 little doubt, I think, that we have in the beds, now briefly 

 described, the base of the Cambrian series of the Mount Lofty 

 and associated ranges. 



The general strike of the beds follows a north-by-east 

 direction, through the Mount Lofty and Barossa ranges, and 

 can be studied in tlie following localities : — (a ) the Inman 

 Valley; fh) in the ranges, a little east of Myponga; fcj on 

 the Onkaparinga, a little below Hack's Bridge, at Mylor ; 

 fd) at Aldgate, Stirling, and Carey's Gully; (r) on the 

 southern spurs of Forest Range, between Summerton and 

 Balhannah ; ff) on the River Torrens, near the confluence of 

 Sixth Creek, and through Houghton; (g) on the South Para, 

 near Menzies' Barossa Mine ; (kj on a line, rather more to the 

 east, forming escarpments of the Barossa Ranges, south-east 

 of "Williamstown ; fij and at Tanunda. There is also a con- 

 glomerate at Hog Bay,"^ Kangaroo Island, which is about on 

 the same line of strike with the outcrops already referred to, 

 and may represent the same horizon. 



As illustrative of the general features of these beds a few 

 of the outcrops will be briefly described. 



Aldgate. — In this locality the basal beds are mostly 

 gritty sandstones, with white felspathic cement, jDassing at 

 times into coarse grits, with occasional pebbles. The stone is 

 soft to friable. A special feature of the stone (as it is of most of 

 the beds at this horizon) is the occurrence of ilmenite grains, 

 which are laid down along current planes or diffused through- 

 out the stone. Current bedding is common. Joints irregu- 

 lar. Much strain is exhibited by the texture of the stone, as 

 well as by frequent small faultings of the body of the stone, 

 which is only made apparent by the dislocation or faulting 



* Tate : Trans. Roy. Soc. South Aus., vol. vi. (1882-83). p. 122. 

 Howchin : Ih'id., vol. xxvii. (1903), p. 82. 



