president's address. — SEQTION c 163 



the probability that physical conditions of varying character may have 

 been the contributing cause of the lithological and organical dis- 

 parities. 



" If the position of the Eocene in the Croydon bore be due to a 

 downthrow fault, then it might be reasonably expected that the very 

 distinctive Eocene series of the Kent Town bore would be repeated in 

 the Croydon bore ; but, as such is not the case, I am of opinion that 

 there is no direct evidence of a fault, and that the Kent Tov/n series 

 belong to a later period, and are more littoral in their organic contents. 



" The series of events that these sections teach us may be summar- 

 ized as follows : — -The Post-Cretaceous sea laved the base of the now 

 subterranean escarpment of over 2,000 feet in vertical height, and at 

 that measure the land stood relatively higher. Deposition and depres- 

 sion were synchronous over the submerged plain ; coincident therewith, 

 wholly or in part, lacustrine and paludinal accumulations, preserved 

 in the carbonaceous beds of the Kent Town bore, were formed on the 

 higher ground. Finally, depression submerged the terrestrial surfaces 

 at Kent Town, and a more littoral life prevailed there in comparison 

 with the earlier Eocene deposits. The miocene deposition followed, 

 succeeded by the extensive denudation of the Miocene and higher 

 levels of the Eocene, and the removal of about 800 feet of the Eocene 

 series, constituting the Adelaide plain. Over this plain of marine 

 denudation, Pliocene marine beds were accumulated, these of a more 

 or less shallow-water origin, and over an area of depression ; finally 

 •to be converted into a vast lacustrine area, in which land drifts of about 

 400 feet have been accumulated." 



Tate's theory of a considerable erosion of the lower marine beds, 

 that has reduced their thickness within the area of the Gulf, is quite 

 consistent with the views now advanced, and, indeed, has been applied 

 in this address to account for the absence of the i; iocene, as well as 

 the hiatus that occurs in the section between the lower cainozoic 

 marine beds, and the fossiliferous pliocene that rests upon the former. 

 Whilst admitting the point for which Tate contends, the phenomena 

 concerned cannot be fully explained without assuming the concurrent 

 action of earth movements that led to the development of a vast 

 graben, or rift valle}^ the depth of which was, probably, not reached 

 by the Croydon bore, as that bore was situated on the side of the 

 valley and marginal to the ranges. 



Confirmatory evidences of the existence of such a trough can be 

 gathered from several sources, in addition to those already adduced. 

 The upper steps of this great trough fault are within range of actual 

 observation. The foot-hills of the Moimt Lofty Ranges take their 

 form from a downthrow, parallel to the strike. The strike of the beds 

 is approximately north and south, and they consist chiefly of a thick 

 quartzite (1,000 feet), which is overlain by an equally thick series of 



F 2 



