244 



may be regarded as the crest of a wide anticlinal fold, nearly 

 flat on top, with a low dip to the south-east on its eastern 

 side ; and a gradual slope with a dip to the south-west on its 

 western side — the dip slope trending towards the Glen Osmond 

 road. The summit of Mount Lofty, especially on its western 

 face, is composed of crags of large size, which rise steeply from 

 the road to a height of 150 feet. The east side of the ridge 

 is steeper than the western, and cuts off the qiiartzite some- 

 what abruptly, the base of which is seen near the bottom of 

 the escarpment, where it gives place to a compact slate, fre- 

 quently coloured red. The line of junction between the 

 quartzite and slate is marked by several springs, which yield 

 strong runners of water. 



The best exposure of the quartzite is seen in Hardy's 

 quarry, on the east side of the ridge, near the road which con- 

 nects Crafers and Piccadilly, and from which most of the 

 road metal of the district is obtained. The top beds are soft, 

 from the effects of weathering. The main body of the stone 

 is siliceous, much jointed, and breaks with a free fracture. 

 The bottom beds in the quarry contain a proportion of crys- 

 talline silicates, of a kind that alters the grain and makes the 

 stone tenacious and tough, and difficult to break. This fea- 

 ture is mainly seen on the west side of the quarry, where the 

 beds show the effects of thrust, directed from the east, which 

 has raised the beds into a succession of small saddles, with a 

 talcose film between the layers. 



Stratigraphy of the Thick Quartzite. — The evidence 

 seems to be conclusive that the prominent outcrops of An- 

 stey's Hill, the Black Hill, the Fourth Creek Hilk'Stonyfell. 

 and Mount Lofty represent the same geological horizon. If 

 so, they are examples of block-faulting on a large scale. A 

 very thick series of beds has been tilted, broken into large 

 fragments, and rendered discontinuous by a deformation of 

 the earth's crust. This conclusion has been reached partly 

 by the correspondence which these quartzite blocks show to 

 each other in their lithology and great thickness, but more 

 particularly from the peculiar occurrence of the "blue metal" 

 limestone which accompanies them. This limestone appears 

 to be in its normal position on the Glen Osmond road and at 

 Beaumont, where, respectively, it is inferior in position to 

 the Glen Osmond quartzites, and superior to those of Mount 

 Lofty. 



In the same way, along the foot-hills, the ''blue metal" 

 limestone at Beaumont, stands related to the Slape's Gully 

 quartzites : the same beds at Stonyfell and the olive planta- 

 tions are stratigraphically associated with tlie Stonyfell 



