579 



7. The structure of Mount Remarkable, when considered 

 as a whole (possessing, as it does, a hard core or backbone 

 surrounded on all sides by sunken areas consisting of newer 

 sediments), supplies a very fine example of a mountain horst. 



8. The tectonic movements that gave Mount Remarkable 

 its peculiar features were not limited to that particular area 

 or produced isolated effects. A continental movement 

 (epeirogenic) first gave a general elevation to the land, which, 

 after reaching a maximum altitude, broke up into regional 

 blocks, which respectively became fissured, tilted, and in 

 places separated from each other by areas of greater subsid- 

 ence. In this way the present physical outlines of South 

 Australia took shape. By the subsidence of the rift-valleys 

 along the lines of the great gulfs the southern Flinders 

 Ranges became scarped to the west; and by the subsidence of 

 a great earth-block that has formed the Willochra plains to 

 the eastward, Mount Remarkable has been scarped to the 

 east. The geological history of Mount Remarkable is, there- 

 fore, only one among many episodes of a like kind in a wider 

 field, where the tectonic forces have operated in shaping the 

 hills and valleys of our land. 



9. The geological age in which Mount Remarkable took its 

 present form cannot h'ave been very remote. The crush that 

 was incidental to the great subsidence came later than the 

 period that witnessed the intrusion of igneous dykes, for the 

 latter were caught in the same mill that pounded the sedi- 

 ments that these dykes had penetrated. The absence of 

 quartz veins from the crush-rock also indicates superficial 

 movements, and proves that there were no deep-seated frac- 

 tures or welling-up of silicated waters that would otherwise 

 have filled up the interstitial spaces caused by the crush. 

 There is little doubt that the southern Flinders Ranges, of 

 which Mount Remarkable forms a part, were elevated as part 

 of the great plateau-forming movements that occurred some 

 time during the later Cainozoic age, and formed the first stage 

 in the development of the southern highlands of South Aus- 

 tralia. The fractures and block-faulting that followed broke 

 up the peneplain into platforms, scarps, and rift-valleys, 

 among which Mount Remarkable took its place. 



10. The plains on the eastern side of Mount Remarkable 

 form the watershed of the Willochra Creek, which carries the 

 main drainage of the district and flows northward. On most 

 of the low rises between the mount and Booleroo Centre, and 

 even further, there are highly-siliceous consolidated river 

 sands and gravels which have no relation to the existing 

 channels. Wells sunk on the. plains prove the existence of 

 alluvium to considerable depths. Thick consolidated gravels 



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