BY H. I. JENSEN, D.SC. I5J 



are better near the shore where sediments may bury 

 them, and where the high pressure of deeper levels does 

 not exist and exert great solvent power on the objects 

 deposited. It is, therefore, axiomatic that the greatest 

 thickness of sediments and the greatest profusion of 

 fossil remains occur within 150 miles of the coast. 



The nature and distribution of sediments of various 

 ages, therefore, gives us a clue as to the position of the 

 shorelines of these ages. A glance at the maps on the 

 following pages should convince anyone that prior to the 

 Tertiary period, Australia had a much different outline 

 from that of to-day, and that the geographical unity of 

 Australia begins with the Tertiary. [1] 



II. PALiEOGEOGEAPHIC STUDIES. 



(a) Pre-Cambeian. 



By referring to the map {Fig. 1) we see that the 

 known Pre-Cambrian areas of Australia are all grouped 

 in the western portions of the continent and Tasmania. 

 A curve drawn from the north-east corner of Tasmania 

 to the Kimberley district of West Australia, with a 

 slight convexity to the north-east embraces all the 

 b,est known Pre-Cambrian areas of Australia. Such a 

 curve, it is interesting to notse, would have its centre near 

 Kjerguelen Island, in the Southern Ocean. But, as the 

 Pre-Cambrian is a geological scrap-heap for all the for- 

 mations which antedate the appearance of life on the 

 earth, rocks of that age must underlie all later formations, 

 and they cannot be utilised in the reconstruction 

 of Pre-Cambrian geography. All that we can say is 

 that both sea and land were in existence in this great 

 epoch, for the Pre-Cambrian rocks are largely of sedi- 

 mentary origin. 



The principal Pre-Cambrian areas of Australia 

 are (1) the West Tasmanian area ; (2) Yorke's Peninsula, 

 West of Adelaide ; (3) the Musgrave Ranges and part 

 of the Victoria Desert, South Australia ; (4) an area 

 near Broken Hill ; (5) the Macdonnell Ranges, South 

 Australia ; (6) the Kimberley Area, West Australia, 

 and (7) the Coolgardie and Kalgoorlie areas, W.A. The 

 igneous rocks of this early period comprise both acid 

 and basic varieties. The acid rocks consisted of granites^ 



