28 



beds are thrown to a position transversely to the former 

 strike, causing the limestone to cross the creek, and it then 

 follows the top of the range on the eastern side, in a return 

 direction. The beds are, apparently, faulted and repeated 

 along the strike. 



At the main angle of disturbance there is a great 

 intrusion of quartz dykes and veins, and the limestone, which 

 follows the eastern ridge, is extensively penetrated with a 

 dark-coloured chert. The chert sometimes occurs in bands 

 several inches in thickness, but, for the most part, in fine 

 laminae, and follows the grain of the limestone, producing 

 a finely-laminated cherty-calcareous rock. 



In the north-western angle of Section 3 (Hundred of 

 Kooringa), the New East Burra Mine (late Utica) is situated. 

 The lode occurs in the limestone and carries copper sulphides 

 and carbonates thinly distributed through a gangue of calcite 

 and barytes. On the western side of these workings the 

 infiltration of silica, in the form of chert, follows the planes 

 of bedding in a fine lamination, which is locally much 

 contorted and is sometimes concentric in form, suggestive of 

 Cryptozoon structure. A careful examination of the ground, 

 however, leaves no room to doubt that this structure is of 

 inorganic origin. The effects of the siliceous infiltration can 

 be traced over a very wide area, from its occurrence in the 

 form of parallel and straight lines ; gradually passing, first 

 into a wavy modification of these lines, and then, in places, 

 to a cyclical and concentric structure. These features occur 

 both along, and for many yards across, the strike. 



In the case of Cryptozoon, the supposed organic struc- 

 ture is quite distinct from the matrix, while in the case 

 under review, the wavy structure is a feature of the rock- 

 mass as a whole and can be explained by a process of 

 metasomatism in which the limestone, along certain layers, 

 has become altered to chert. The immediate cause of such 

 a change can be explained as a consequence of the powerful 

 local strains to which the bedding has been subjected by 

 earth movements, and the introduction of silicated waters. 



At the Burra the same limestone shows laminated and 

 imperfect concentric structures, but without the introduction 

 of silica and with a less resemblance to Cryptozoon. Cherty 

 inclusions are first noticed in the limestone, along the 

 strike, about a mile to the south-eastward of Kooringa. (See 

 Howchin, "Autoclastic, Intraformational, Enterolithic, and 

 Desiccation Breccias and Conglomerates," Roy. Soc. S. Austr., 

 vol. xliv., pis. 17 and 18.) 



