244 Frederick Chapman : 



Ejrisodts in the Formation of the Beds of the Great Bight Area. 



In pre-Miocene times the area abutting on the Cretaceous of 

 the Lake Eyre district to the north-west, to Charlotte Waters on 

 the north, to Albany, on the west, and to the Adelaide Plains on 

 the east, and far to the south on what is now the Southern Ocean, 

 was probably dominatedi by an estuarine or generally base-levelled 

 country. This area also extended through the Riverina as far as 

 Wagga, in New South Wales, and occupied a large part of the 

 Wimmera and Mallee districts of Victoria. The underlying 

 (fundamental) rocks of this area consist mainly of granite,'^ 

 chloritic slate, felspathic quartzites, slaty rocks and sandstones, 

 all excepting the granite possibly referable either to the Ordo- 

 vician, Cambrian or metamorphic series, including Algonkian. 

 The deposits laid down on these basal rocks were river, estuarine, 

 swamp and lake accumulations, consisting of sands and clays with 

 <:-arbonaceous and lignitic material. 



Following the deposition of these beds, which, by the way, were 

 not uniformly spread over the entire area mentioned, there were 

 occasional oscillations which brought them below sea-level, causing 

 an interstratification of marine beds with the terrestrial. Later, 

 the oscillations ended in a steady to quick downward movement 

 until a depth of at least 100 fathoms below sea-level was reached. 

 In this sea-bed a rich deposit of calcareous mud w^as formed, filled 

 with debris of polyzoa, echinoids, moUusca and foraminifera. 

 These beds can be referred to the Janjukian series of Victoria, and 

 are homotaxial- with the Miocene of Europe. 



In Lower Pliocene times (Kalimnan series) the sea-bed rose to 

 within a few fathoms of the surface, with fine sandy deposits, 

 upon which flourished molluscs as Ostrea, Natica, Tur^itella and 

 the sea-urchin, Laganum, amongst many other organisms. In 

 places there were huge oyster banks, and in the more rocky parts 

 vast deposits of mollusca peculiar to such conditions, as Mytilus, 

 Barnea, Veneriipis, Area, CucuUu^ea and Glycimeris, a few species 

 of which facies are still living. Possibly a part of the Miocene 

 limestone of w^hich the fauna is here discussed, may have per- 

 sisted into the Low^er Pliocene, as evidently a few forms, such as 

 Tellijia cf. alhinelloides and Laganum, seem to indicate. 



In the later period of the Pliocene this sea-bed again deepened, 

 and a shell deposit with many existing species was laid down. 



7. In the Albany district these older limestones ^Plantaaenct Beds) have been shown 

 hy J. T. Jntson and E. S. Simpson (Journ. and Proc. Roy. See. W. Australia, Vol. II., 

 1917, p. 48) to have been laid down on tlie granite. 



