president's address. — SECTION G. 155 



evidence points in the direction that the loas by denudation has been 

 very considerable. The Adelaide section, taken jointly from the 

 Kent Town and Croydon bores, is, probably, most intact, but is evidently 

 far from complete. 



The late Professor Ralph Tate* estimated the thickness of the 

 fossihferous Eocene of the Croydon bore to be 921 feet, with a possible 

 45 feet more. The fragment of fossihferous Eocene preserved on a 

 ledge of Cambrian rocks penetrated in the Kent Towii bore.f near 

 Adelaide, has a thickness of 91 feet, J which Tate regarded as higher in 

 the series and more littoral in character than the beds penetrated in 

 the Croydon bore. It seems most likely that the Kent Town beds 

 represent a late stage in the deposition, and were the result of an 

 overlap and transgression by the sea over the lacustrine area which, by 

 a downward movement, gradually passed below sea-level. When 

 added together, we find that the Croydon and Kent Town sections give 

 a total thickness of at least 1,070 feet, but presently we shall be able to- 

 show that even that part of the series which has been more or less 

 protected by a downthrow, in the formation of the St. Vincent's trough, 

 had undergone great erosion in the pre-Pliocene times, and thereby 

 reduced the apparent thickness of the beds. As the base of the Eocene 

 marine beds at Kent Town is separated from the upper limits of the 

 same beds in the Croydon bore by a vertical difference of about 700 feet,, 

 on the theory stated above, these figures would represent the maximum 

 possible loss of these beds by denudation if we regard the Kent Town 

 and Croydon readings as parts of one and the same section. 



The fragments of lower Caiuozoic beds outcropping along the shores 

 of Gulf St. Vincent evidently rest on the same shelf of Cambrian rocks 

 as the Kent Town beds, and must be correlated with these, as they have- 

 a general agreement with the latter as to altitude, fossil contents, and 

 littoral conditions in deposition. This is typically the case with the 

 Aldinga Bay beds, which show a great variety of sediments, and change 

 materially within short distances. Tate says of these beds — " It is 

 impossible by words to adequately convey to the mind the changing 

 nature of the Eocene sediments composing this section." He then 

 gives a detailed account of numerous sections exposed in the sea cliffs, 

 within a few miles, in illustration of their lithological variation. § 



The Eocene beds make no prominent features in the physiographical 

 outlines of South Australia. They form level country at low altitudes. 

 With the exception of the Nullarbor Plains, at the head of the Great 

 Australian Bight, and the Murray Plains, and parts of the south-east,. 



• Trans. Roy. Soc. S. Aus., Vol. XXII, p. 196. „ , ,, 



t "Notes on the Tertiary Strata beneath Adelaide," Trans. Roy. St-c. 3. Aus., Vol. V, 



p. 40. Ibid., Vol. XXII, p. 197. 



{ See footnote in seq. _ _, _ 



§ Tate on " The Correlation of the Marine Tertiaries of Australia," Part III, Trana. Roy. 



Soc. 3. Au3., Vol. XX., pp. 122-12i. 



