160 president's. ADDRESS. — SECTION C. 



longitudinal valleys of erosion which still connect the interior of the 

 continent with the south coast, but fail to carry the present drainage. 



Earth movements that followed the uplift (or were developed as 

 isostatic equivalents of such an uplift) have profoundly altered the 

 features of the country, and changed both its drainage and its climate. 

 No important folds were developed by these earth movements — indeed, 

 the rocks were placed at high tension by the uplift, and ultimately 

 formed adjustments by warping, fracture, and settlement. 



The original plateau of uplift has been greatly modified by sub- 

 aerial denudation and by faulting. The old peneplain is •still clearly 

 distinguishable in the flat-topped hills which in the Mount Lofty 

 Ranges have an average elevation of about 1,500 feet, and from which 

 rise the greater heights of Mount Lofty (2,334 feet) and Mount Barker, 

 as monadnocks. This old plateau has been greatly incised by river 

 action, that has, in places, exposed the pre-Cambrian basement. The 

 streams are small, but numerous, and flow through gorges 300 feet to 

 500 feet deep, and are mostly in a juvenile stage of development. In 

 places, very conspicuous horsts have been left by the subsidence of the 

 surrounding areas — as, for example, the Hogshead, near Pekina, and 

 Mount Remarkable, in the southern Flinders Ranges. 



The Mount Lofty Ranges are bounded by fault scarps, both on their 

 eastern and western flanks — especially the western — where they pass, 

 by a series of shelvings or steps, down to the deep graben of Gulf 

 St. Vincent. This is a feature not confined to the Mount Lofties, as 

 the Willunga, the Barossa, and the Flinders Ranges show similar 

 step-faulting, associated with large transverse fault planes, which have 

 cut up the hill country into immense angulated blocks, and these major 

 earth segments are again broken up into secondary fault blocks. Of 

 these may be mentioned — {a) the Willunga major segment, with the 

 fault scarp of the Willunga Ranges, forming an obtuse angle with the 

 coast scarp that borders the throwdown to the gulf ; (6) the Mount 

 Lofty segment, with its eastern scarp-face, near Summertown and 

 Piccadilly, its throwdown in the piedmonts of the western side to the 

 great trough of the G-ulf, and its gradual slope southwards to the 

 base of the Willunga Ranges ; (c) the Barossa segment, with its pro- 

 minent western scarp, in two steps ; and (d) the southern Flinders, 

 with a bold and precipitous scarp, facing the Gulf, and its return (at 

 nearly right angles) in an easterly direction, forming the Crystal Brook 

 Ranges. In this magnificent field of block-faulting (and our illustrations 

 might have been extended to many others equally well defined), we 

 must limit our attention mainly to one segment, viz., the Mount Lofty, 

 which may be taken as the type example of the class. 



We have already seen that the 1,500-ft. level in the Mounty Lofty 

 Ranges represents the remnants of the peneplain of the original 

 uplift now extensively dissected. On the western side of this peneplain 



