540 



Physiographic. 



The Nullarbor JPlain is an area of limestone country 

 extending westward from Fowler Bay to beyond Eucla in 

 Western Australia. Its east- west extent is 450 miles and 

 its greatest nortli-soutli width about 200 miles. The area 

 within South Australia is 17,767 square miles, throughout 

 the whole of which there is no watercourse or lake. It is 

 underlain, however, by the Eucla basin of artesian water 

 which has been tapped by bores at depths varying from 

 298 ft. -to 1,500 ft. A bore sunk at Ooldea gave water at 

 480 ft., containing 7*716 ozs. of salt to the gallon. d) 



Little has been written on the geology of the area, the 

 account by Tate, (2) who visited the seaward margin of the 

 Nullarbor Plain in 1879, being still the most complete. 



The Nullarbor Plain forms a part of the Bunda 

 Plateau*, which, according to Tate, is the ''elevated bed of 

 the older Tertiary sea, the sediments of which were deposited 

 within a very extensive granitic basin." These igneous rocks 

 come to the surface at various places round the edge of the 

 basin, an outcrop occurring to the east of Ooldea. According 

 to Howchin(3) the limestones are Miocene (Janjukian), over- 

 lain by older Pliocene (Kalimnan), at Wilson Bluff, near 

 Eucla. 



The surface of the plain is not perfectly level, but rises 

 and falls in gradual undulations. ("^^ The limestone is covered 

 by a red sandy loam varying from a few inches to a foot or 

 more in depth, which soil, being fine grained, bakes hard 

 when dry. Fragments of limestone, however, are freely 

 interspersed with the soil, and appear at the surface in most 

 places, especially on the ridges. 



Here and there are "dongas," or slight depressions vary- 

 ing: in area from less than an acre to some hundreds of acres. 

 Tlie dongas are said to be the largest at the western side of 

 the plain. Those seen by us were small; they are said to be 

 infrequent in the centre of the plain. The soil in the dongas 



(1) Rep. 3rd Interstate Conference on Artesian Water, Ade- 

 laide, 1921, p. 16. Adelaide, Govt. Printer. 1922. 



(2) Tate, R., The Natural Histor\- of the Country around the 

 Head of the Great Australian Bight, Trans, and Proc. Philos. 

 Soc. of Adelaide, S. Austr., ii.. pp. 94-128, 1879. 



(3) Howchin, W., "Geology of South Australia," pp. 457 and 

 466, Adelaide, 1918. 



(4) A quantity of interesting information as to the Nullarbor 

 Plain is collected as a supplement to the Presidential Address to 

 the South Australian Branch of the Roval Geographical Society, 

 session 1917-18. Proc. Rov. Geol. Soc. S.' Austr., xix.. pp. 101-153, 

 1919. 



