420 PROCEEDINGS OF SECTION C. 



my late colleague in the Adelaide University, has made a study of 

 these quartzites, and published in the Trans. Royal Society of South 

 Australia an interesting description of a large number of specimens 

 collected from the Mount Lofty Ranges. The main quartzite in this 

 series, which reaches a thickness of 1,000ft., has been broken up by 

 block faulting and forms the disconnected fragments of the Black Hill, 

 Stonyfell, Mount Lofty, and others. The Glen Osmond and Mitcham 

 quartzite is 100ft. in thickness, and occupies a higher position in the 

 series than the last name!. 



The slates and phyllites, which are interbedded with the quartzites, 

 supply the preponderating geological features of the foothills of the 

 Mount Lofty Ranges near Adelaide, and by their decomposition form 

 the rich soils of our agricultural fields, vineyards, and gardens of the 

 lesser slopes and gullies of these ranges. 



Between the Mitcham quartzites on the one side and the Tapley's 

 Hill banded slates on the other there occurs a formation which exhibits 

 strongly contrasted features from either. It forms in its essential 

 characteristics a typical till bed, unstratified, and thickly charged 

 with erratics, many of which are conspicuously striated by ice action. 

 The beds near Adelaide form the southern extension of the great Cam- 

 brian glacial formation which covers a vast area northwards of Ade- 

 laide, reaching within a few degrees of the Tropics. As these beds 

 have received special reference from me in another paper, which has 

 already been placed before the Association through the medium of 

 the Glacial Research Committee, further comment on this subject is 

 unnecessary here. 



The hasal beds of the Cambrian consist of white felspathic grits, 

 arkose grits, and coarse conglomerates, with clastic ilmenite, averaging 

 from 150ft. to 200ft. or more in thickness. They rest on an Archaean 

 complex of highly altered schists and quartzites which have been pene- 

 trated by granitic batholiths, aplites, and pegmatites of various ages, 

 and unitedly are intimately foliated, constituting a very intricate and 

 difficult series for determination. The eroding agents of early Cam- 

 brian times operated on this old Archsean floor, and the basal grits 

 and conglomerates of the overlying Cambrian represent the waste 

 and redistribution of these older rocks. 



The line of junction between the Cambrian and Pre- Cambrian, 

 whilst sufficiently distinct in its broader features, is not always easy 

 to discriminate in particular sections. This follows from the fact 

 that the basal Cambrians are composed of the clastic material 

 gathered from the rocks on which they rest, whilst a subsequent peg- 

 matisation has included both Cambrians and Pre-Cambrians in one and 

 the same conditions of alteration and intrusion. When the great 

 thickness of the Cambrian system of South Australia is taken into 

 account, and the consequent depth to which the beds must have sunk 

 to receive such a weight of material, it is not to be wondered at that 

 the lower members should have reached an isogeotherm where peg- 

 matisation was active. In places the basal beds exhibit flowage in a 

 remarkable degree. Some striking effect3 of this kind are seen in the 



