PROCEEDINGS OF SECTION C. 421 



coarse conglomerates, especially in the Grey Spur outcrop of Inman 

 Valley. In the upper and middle portions of this conglomerate bed 

 the pebbles occur in their normal shapes as they were rounded by water 

 action, but towards the lower parts they gradually become compressed 

 and elongated, as though rolled out, and finally pass into quartz veins 

 parallel with the bedding planes, which have also become planes of 

 thrust and flowage. 



These basal beds follow an axis of elevation which, intermittently, 

 exposes the Pre-Cambrian floor in a north by east direction, from 

 Inman Valley in the south, across the Onkaparinga (near Mylor), 

 Aldgate, Stirling East, Carey's Gully, Forest Range, River Torrens, 

 Houghton, the South Para, Barossa, and Tanunda 



The Eastern Side of the Mount Lofty Ranges. 



There still remains the question as to the age and succession of the 

 beds which occur on the eastern side of the Pre-Cambrian axis. 



A prominent feature of the eastern slopes of the Mount Lofty and 

 related ranges is the development of a great plutonic and igneous area, 

 which takes in not only the eastern side of the highlands, but extends 

 over the Murray Plains and much of the continental shelf of the 

 southern coast. It forms a plutonic area of great complexity, and along 

 its western margin numerous basic dykes and pegmatitic areas intersect 

 sedimentary beds that show a prevailing easterly dip. A regional 

 metamorphism, of a high degree of intensity, sets in gradually a few 

 miles east of Mount Lofty (and also of the Pre-Cambrian axis), and 

 reaches its chmax in near association with the great granitic region on 

 the east. But little detailed work has been done on this much-altered 

 and difficult tract of country. There is reason to believe that the beds 

 on the eastern side are the equivalents of those that outcrop on the 

 western side of the Pre-Cambrian axis. The chief considerations which 

 have led to the adoption of this view are : — 



(1) The dip on either side of the Pre-Cambrian axis of elevation 

 is complemental in its direction. The prevailing dip of the beds on the 

 western side of the axis is toward the west, and on the eastern side 

 towards the east, forming together a great anticlinorium, which requires, 

 for stratigraphical consistency, that there should be a repetition of 

 beds on the opposite limb of the fold, not necessarily maintaining a 

 lithological resemblance, but as equivalents in the order of succession. 



(2) The basal conglomerates and ilmenite grits of the Inman Valley 

 have a dip to the east, and .exhibit in superposition a series of quartzites 

 and slates, which become more schistose in their upper members as 

 they approach the great granitic zone of the coast, at a distance of 

 seven miles from the base. In this instance it seems clear that the beds, 

 which are superior to the basal conglomerates, must be the equivalents 

 of those that overlie the same basal beds on the western side of the 

 Pre-Cambrian ridge, and their occurrence can be traced uninterruptedly 

 to the region of intrusion. 



