107 



gravels referred by Professor Tate to the Upland Miocene. '8> 

 They consist of coarse gravels and sands. On physiographical 

 grounds it seems difficult to regard them as Miocene, for they 

 are bedded against the side of a scarp produced by a most 

 recent uplift. It seems more likely they were produced by 

 a river which flowed down the fault-block before described 

 and along the foot of the scarp. They are probably of more 

 recent origin than the high-level gravels mentioned above. 

 This gravel is covered by the usual "Upland Miocene'" flora 

 and soil. 



Summary. — It will be seen from the above that there 

 have been in the history of the Mount Lofty Ranges, as re- 

 vealed by the Houghton geology, at least three periods of 

 :great earth movement : — 



(a) The Pre-Cambrian, contorting and modifying the 

 schists, and possibly consequent on the plutonic 

 intrusion. 

 (h) The Post-Cambrian, but (from evidence in the 

 southern portion of the range) early Palaeozoic 

 period of crust-folding broiight about by an over- 

 thrusting pressure from the east. Except in minor 

 details the movements of the strata have not in- 

 fluenced the present topography, but are revealed 

 chiefly by stratigraphical dislocations. These may 

 then be termed the periods of stratigraphical 

 faulting. 

 (c) It is the folding and faulting during the late Ter- 

 tiary period that has so profoundly influenced the 

 present topography, forming miles of fault scarps 

 or wide areas of tilted peneplains. To the fault- 

 ing of this period the term physiographic faulting 

 may well be applied, for it is on physiographical 

 data almost entirely that the faults are recognized. 

 It is worthy of note that in each of these three periods 

 •oi crust movement the axis of folding or faulting was almost 

 a meridional one. 



Brief Notes on Other Areas in which Pre-Cambrian 

 Rocks have been noted similar to those of Houghton. 



Barossa and Hum,hug Scrub. — A large area here, partly 

 overlain by the "Upland Miocene" gravels that carry the allu- 

 vial gold, is made up of an augen gneiss whose "eyes" are 

 crystals of potash felspar. In working up the creeks that 

 flow westerly from these hills a gradual increase in the size 



(8) Presidential Address, Phil. Soc, S.A., 1878-9. 



