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Caroona Hill (Lake Gilles). 



By W. L. Clelakd, M.B., Edin. 



[Bead June 7, 1887.1 



LocaJHy. — Caroona Hill is the southern extremity of a range 

 about seven miles in length running a little west of north. It 

 is forty-five miles due west of Port Augusta, and twelve miles- 

 east of the head of Lake Gilles. 



There are two points of interest in connection with the 

 locality — (1) The existence of polished rock-sarfaces on the 

 highest elevations of Caroona Hill ; (2) The scanty but definite 

 distribution of the subterranean water fit for consumption. 



Geological Surroundings. — To the eastward an undulating 

 plain of Tertiary age (H. T. L. Brown, Eeport, June, 1885) 

 extends for twenty-four miles to the nearest hill of the " Lin- 

 coln Grap" formation. To the westward a similar plain ex- 

 tends for upwards of seven miles to various outcrops of granite. 

 The plains are formed of a decomposed granite mixed with 

 sand and quartz and ironstone pebbles, the whole strongly im- 

 pregnated with gypsum. 



To the southward is a range composed of red haematite and 

 manganese ore, stretching away towards Mount Middleback, 

 distant some thirty miles. The northern extremity of this 

 range presents a remarkable appearance, and is known as the 

 "Iron Knob." The rocks are in rectangular blocks of many 

 tons in weight, and piled confusedly upon one another. In size 

 and shape they bear a forcible resemblance to the blocks of 

 stone of which the pyramids near Cairo, in Egypt, are built. 

 The structure of the ore is crystalline, and presents a steel- 

 like fracture. 



To the northward are hills of quartzitic porphyrite and 

 granite, reaching as far as the Gawler Eanges. 



Physical Features of Caroona Sill Hange. — The western side 

 rises abruptly and almost perpendicularly from the plain to a 

 height of from four to five hundred feet. It consists of a red 

 sandstone, with well-marked stratification. The dip of the 

 strata is 30 deg. and eastward. The strike is also well- 

 defined, running almost due north and south, the range trending 

 in the same direction. 



Abutting unconformably against this sandstone on the 



