76 



'Of a cbaiu of granite and other igneous rocks running in a nortli- 

 westerl}^ direction from the extremity of Eyre Peninsula 

 to the Gawler Eanges ; also of another chain of Palaeozoic 

 rocks — the present Flinders Eange — running nearly parallel to 

 the eastward. Between the two is the " Lincoln Gap" forma- 

 ■tion, resting probably on a Palaeozoic blue clay-slate. If this 

 *' Lincoln Gap" formation at one time extended between the 

 i;wo ranges, it would have formed an effectual barrier to dam 

 back the waters to the north, and thus convert the present 

 Lakes Gairdner, Torrens, and Eyre into one continuous shallow 

 sea of several hundred feet deep. It would also have sufficed 

 to submerge the beds of fossil leaves found at Mount Eba to 

 -the west and Bottle Hill to the east. In such a case Caroona 

 Hill Eange most probably formed a portion of the western 

 margin of the " Lincoln Gap" formation. The presence of the 

 i;hick deposit of conglomerate suggests that at that time the 

 natural outlet for the waters was at this point, the sub- 

 angular character of the pebbles forming the conglomerate, 

 pointing rather to a fluviatile than to a littoral origin. Subse- 

 quently to this there was probably the upheaval of the land 

 -during the Pliocene period, to which Prof. Tate refers in his 

 Presidential Address (1879), when the land was elevated into 

 " regions of perpetual snow." If on the subsequent subsidence 

 of the southern boundaries of the continent this took place 

 unequally, as might very possibly be the case in the proximity 

 ■of the igneous formation of the Gawler Eanges, the sandstones 

 abutting against it would become tilted ; and the ancient river, 

 being thrown more to the eastward, would find an outlet in the 

 valleys referred to by Mr. Brown. The ancient river-bed at 

 Caroona Hill would then for a longer period form possibly an 

 outlet for some glacier from the adjoining granite mountains. 

 This theory would also account for this particular remnant of 

 the Caroona Hill Eange being higher than the "Lincoln Gap" 

 Tiills to the east. 



The absence of organic remains in the " Lincoln Gap" for- 

 mation makes it difficult to determine its geological age, which 

 at present can only be inferred. Considering the proximity of 

 the Palaeozoic clay-slate of the Flinders Eange to the eastward, 

 and the occurrence of a clay- slate in the two wells sunk on the 

 plain to the westward, an inference might be drawn that this 

 ■clay-slate forms the bed-rock of the " Lincoln Gap" sandstone. 

 If this be correct it would make this sandstone somewhat 

 analogous in position to the sandstone capping of Mount 

 Brown. It would also make it probably different in geological 

 .age to the " desert sandstone" to the north, which is underlain 

 by a formation proved to be of Mesozoic age. 



JPoJislied Swfaces. — These are limited to the conglomerate 



