162 president's address. — section c. 



about 1,220 feet below the Belair platform. This may be called the 

 Adelaide platform, resting on which are the older cainozoic marine 

 beds, proved by sinkings at Adelaide, Campbelltown, Paradise, and 

 Klemzig. These buried outliers occur at or about sea-level, and there- 

 fore correspond as to altitude mth the same beds seen on the shores of 

 the Gulf at Noarlunga, Aldinga,and Sellick's Hill, and we may reason- 

 ably conclude that they all rest on the same shelf of old rocks. 



Fourth Fault-Plat form. — The fourth fault-shelf was revealed by the 

 Croydon bore (situated about 3 miles west of the Kent Town bore), 

 where the platform of cambrian rocks was proved at a depth of 2,206 

 feet below sea-level. Here, again, as in the case of the Kent Town 

 bore, fluviatile and marine beds of lower cainozoic age rest upon a 

 Cambrian platform. 



In the strongly contrasted altitudes of the older cainozoic beds 

 we have a clear proof of differential movements, which have determined 

 the vertical position of the dismembered marine sediments. This 

 has occurred, not only from secondary faultings that transpired 

 Avithin the limits of the major displaced blocks, but also in the strati- 

 graphical discordance of one faulted block as compared with another. 

 Thus, in the Willunga faulted segment there is a small outlier of the 

 older marine series on the top of the Hindmarsh tiers, some 900 feet 

 above sea-level, while on the adjoining Mount Lofty faulted segment 

 (sloping to the base of the Willunga scarp) the same lower marine 

 beds occur in three patches, one on the sea coast ; the second, 4 miles 

 distant, near Bellevue, 250 feet above sea-level ; and the third, in a 

 further distance of 3 miles to the north-east, at 600 feet above sea-level.* 

 We have, therefore, within the area of a few square miles, four small 

 patches of the same fossiliferous rock, on successive steps, ranging from 

 sea-level up to the main plateau of the highlands, at 900 feet above 

 8ea-level. If we take in a wider field for comparisoi^ between the 

 highest platform carrying the lower marine beds on the Hindmarsh 

 tiers and the cambrian platform carrying the same series at the bottom 

 of the Croydon bore, there is a vertical difference of 3,100 feet. 



These interesting structural features can scarcely be explained 

 on any other hypothesis than by assuming the existence of a fault- 

 trough on a large scale in the valley of Gulf St. Vincent. It is true 

 that the late Professor Tate called such a theory in question, and gave 

 a different interpretation to the Kent Town and Croydon sections. 

 He states, t " Professor David and Mr. Ho wchin have sought to explain 

 the stratigraphical relationships of these two dissimilar series of beds 

 by the introduction of a north and south fault, ranging along the 

 buried scarped front of the Archaean rocks, on which the Eocene and 

 Miocene of the Adelaide plateau repose. This conjecture disregards 



* Tats, " Eocnne of Aldinga B.iy." Trans. Roy. Soc. S. Aus., Vol. XX, p. 121. 

 t Ihid.. Vol. XXII, p. 197. 



