125 



are bounded on the ocean side by a granite dyke of vast propor- 

 tions. The prevailing dip is eastward, and they in all likeli- 

 hood pass under the tertiaries which occupy the surface of the 

 country eastward of the lakes ; in fact, their presence at no in- 

 considerable depth has been proved on the estate of Mr. Mac- 

 Parlane at Wellington Lodge. The existence of petroleum in 

 this region is in the highest degree problematical. The pros- 

 pectus of the Coorong Oil and Coal Company, October 21, 1875, 

 contains a grave error, which must have proved a snare to the 

 ill-informed on geological matters, though at the same time it is a 

 tacit admission that geological teachings are applicable to the 

 search for coal. The passage reads : — " Borings have been put 

 down to a depth of 75 feet, from which depth fossil shells have 

 been raised, indicating a carboniferous formation^ The fossils 

 which were shown to me by one of the promoters prove to be of 

 Miocene age, as might have been anticipated from surface 

 indications. 



The exploration for petroleum at Mount Crawford is still more 

 at variance with geological induction, for whilst in the former 

 case we do not know what actually underlies the Tertiary cover, 

 nor the depth and character of the overlying strata, yet we do 

 know that in this one search is conducted in highly metamor- 

 phosed rocks, as may be inferred from the words of Ernie 

 previously quoted. 



In the Lower Silurian, the formation next in time repre- 

 sented in South Australia, we have evidence of the existence of 

 marine life, and the colour of the black Ardrossan limestones 

 is seen to be due to diffused animal matter, though as regards 

 amount it can only be viewed as a petrological novelty. 



The Jurassic rocks which occupy the low tracts west and 

 south of Lake Eyre may possibly be proved to contain car- 

 bonaceous or bituminous beds ; but our knowledge of them is 

 so meagre that we have no warrant to speculate further upon 

 the probability of finding coal, oil shales, or petroleum in 

 them. 



The Miocene rocks, which have been fairly well examined in 

 natural and artificial sections, present for the most part 

 arenaceous and calcareous clehris of marine origin, and are un- 

 promising as a source of coal or petroleum. The Upland 

 Miocenes, occupying as they do isolated areas of very limited 

 extent and thickness, cannot possibly furnish workable coals, 

 though lignites and carbonaceous muds may not unreason- 

 ably be expected to be met with among the thicker deposited 

 strata. The same remarks are applicable to the " Desert Sand- 

 stone." 



The Pliocene drifts which have levelled up to considerable 

 elevations pre-existing broad and deep valleys to form exten- 

 I 



