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material from thin intrusive veins, it is quite possible 

 that the latter may exist in parts of the bavSal grits in a form 

 almost indistinguishable to the eye. I was particularly struck 

 with such a possibility when examining the coarse felspathic 

 grits which rest immediately on the Pre-Cambrian beds near 

 Melrose's, Aldgate. My friend and colleague, Mr. Mawson, 

 B.Sc, discovered a pegmatite vein penetrating the Cambrian 

 glacial till of Sturt Valley, which is at a considerably higher 

 geological horizon than the basal grits. 



There is thus sufficient evidence to show that there was, 

 to a limited extent, contemporaneous pegmatization of both 

 the Pre-Cambrian and the lower Cambrian, and was probably 

 coincident with the maximum depression of the Cambrian 

 series. If the Mount Lofty area received the full thickness 

 of the Cambrian beds, as developed to the north of Adelaide, 

 the depth to which they must have sunk during the period 

 of their deposition must have equalled, if not exceeded, 20,000 

 feet, which would bring them well within the zone of meta- 

 morphic action. 



The Mount Lofty Ranges, through a breadth of from 

 20 to 30 miles, exhibit anticlinoria on a large scale, 

 but, through excessive denudation, the primitive foldings are 

 truncated, and often obscure. The main axis of the uplift cor- 

 responds, roughly, with the centre of the highlands, although 

 the Archaean core often occupies a less elevation than the 

 superincumbent beds. From this ridge of elevation the beds, 

 on the whole, dip away westwards and eastwards. A consider- 

 ation of the causes which brought about the elevatory move- 

 ment must be deferred until the eastern side of the ranges 

 has been studied, and more particularly the great igneous 

 belt which skirts the highlands of South Australia on their 

 eastern and southern sides. It is, however, certain that the 

 great earth-push came from the east, which determined the 

 main north and south direction of the major folds — that is, 

 the main folding has occurred at right angles to the folding 

 forces, and has produced endless small overlaps and thrusts 

 towards the west. There was also a nip between north and 

 south, which contracted the area along the strike and diverted 

 the main folds into a more or less tangential ("irection. This 

 duplex system of crush has caused the beds, in many places, 

 to roll in all directions, giving rise to a periclinal dip, pro- 

 ducing either domes or saucer-shaped depressions. This fea- 

 ture is still more markedly developed in the Flinders Ranges. 

 Small slips and overthrusts frequently occur on the line of 

 strike, and are well seen on the beach between Brighton and 

 CaDe Jervis, where the sea has cut a floor of marine denuda- 

 tion. 



