102 



Physiography, etc. 



Houghton is thirteen miles from Adelaide along the- 

 Gumeracha-Mount Pleasant Road. It is situated on the 

 western edge of the plateau or peneplain that forms the main 

 part of the Mount Lofty Ranges, and above which the higher 

 peaks — Mount Lofty, Mount Barker, Mount Gawler, and 

 others — rise as monadnocks. This area had been reduced 

 partially to sea-level during the early tertiary period, but 

 in comparatively recent times it has been elevated with a 

 slight easterly tilt, considerable block-faulting, and possibly 

 slight corrugation. 



The Torrens Valley appears to antedate this uplift. 

 Mature near its source, it gradually becomes enclosed in an 

 ever-deepening canyon, till it leaves the ranges near the 

 Weir in the form of a fairly young valley, though one in 

 which there is sufficient gradation to allow comparatively long 

 pools between the rapids. The Torrens must, then, have cut 

 its way down, keeping pace with the gradual elevation of 

 the land. The river is therefore an entrenched meander, (2) 

 a conclusion strongly supported by the winding course of 

 the river, and its independence of the geological structure of 

 the country. Except in minor details (^) it is not influenced 

 by the variation in the hardness of the different strata through 

 which it passes. Its tributary creeks, however, often are so. 

 A striking example of this is Deep Creek, running from 

 Highercombe to near the Junction between Sixth Creek and 

 the Torrens. It has cut down in the soft lower phyllite for- 

 mation, while a subtributary that enters it from the east has 

 been hung up by the hard Pre-Cambrian schist, and falls into 

 the valley over a fine waterfall a hundred feet or more in 

 height . 



The Little Para River rises just near the edge of the 

 Torrens Valley, and flows north-westerly across the Pre-Cam- 

 brian intrusion, and is then deflected by the Cambrian 

 quartzites, which it follows for a couple of miles. Finally break- 

 ing across these it strikes westerly in a deep valley, entering 

 more level country near Golden Grove, only to again pass into 

 a young valley, emerging on the coastal plain near Salisbury. 

 It is by the Little Para that most of the sculpturing of the 

 Houghton district has been performed. 



The area between Golden Grove and Salisbury is portion 

 of a triangular area running from near One Tree Hill at Gaw- 

 ler down to North Adelaide. This, like the Blackwood- 



(2) Compare Professor Tate, Trans. Rov Soc, S.A. viii., 

 1884-5, p. 57. ■ ■ 



<■"'' e.ri.. its sharp deflection by the quartzite just west of the 

 weir. 



