57 



T)eing, however, 70 feet above sea level ; but on the western 

 .side of the Older Tertiary escarpment at Adelaide the drift 

 beds are at deeper levels and are projected below low-water 

 mark in Holdfast Bay. In the Port Wakefield bore these beds 

 were bottomed at 312 feet below sea level, and throughout 

 their thickness are highly charged with carbonaceous muds. In 

 -the Stirling bore, near Port Augusta, the base was not reached 

 at 460 feet, corresponding to a depth of 356 feet below low- 

 water mark. Here, also, carbonaceous muds were passed 

 through, and a few fragments of crocodilian scutes were ob- 

 tained. 



It has not been definitely proved that the deposition of the 

 Pliocene Drifts was contemporaneous with the existence of our 

 glaciers, but their mode of occurrence, nature, and organic re- 

 mains imply great aqueous precipitation during the period of 

 their accumulation, and therefore presumably coeval with the 

 glacial phenomena. The view of the lacustrine origin of the 

 drifts of the lowland and upland plains may seem at first diffi- 

 cult of acceptance, because of the necessity for barriers across 

 their lower ends to impound the drainage. Actual barriers are 

 recognisable in a few cases, as that formed by the Older Ter- 

 tiary escarpment at Adelaide, through a gap in which the Eiver 

 Torrens now flows ; a similar feature is seen in the valleys of 

 the Light and Gilbert, near Hamley Bridge. In most of the 

 upland plains the flanking hills converge at the lower end, 

 leading one to suppose that at deeper levels they increasingly 

 approach one another to form a gorge ; but in most cases the 

 great depths to which the old valleys have been filled precludes 

 iill hope of ever learning much on this point. As to the great 

 lake region of Central Australia, the configuration of the pre- 

 sent surface permits of a vast increase in the area and depth of 

 the water in each basin. In the case of the Adelaide Plain, its 

 lacustrine origin demands a barrier across what is now St. 

 Vincent Grulf ; but the truncated margin of the drift around 

 its shores and the depth below sea level to which the 

 drift extends at Port Wakefield, indicate that the gulf has 

 been excavated out of the drift beds. From this and other 

 circumstances it is not possible to restore the configuration of 

 the land surface immediately prior to the glacial period, and 

 therefore the pre-existence of barriers must remain an assump- 

 tion, as also that the building up of terminal moraines may 

 have been the primary cause of the filling up of deep valleys 

 with subaerial detritus. Mr. Scoular argues against any Exte?^- 

 siYE Upheaval OF the Lai^d, because "the drainage of the 

 present river system would have been completely altered." 

 But the fact that the Eiver Torrens has cut its way across the 

 inclination of the strata in deep gorges and contrary to the 



