60 THE ORIGIN OF AUSTRALIA 
of Palaeozoic or older Mesozoic age, and so are a great part 
of the less elevated (500 to 2,000 feet) regions of West 
Australia, and parts of South Australia and the Northern 
Territory. 
14. The rest is covered with Cretaceous and Tertiary 
rocks, with wide areas’ of surface sandy material, which 
may be the waste of Tertiary or Cretaceous beds, or may 
be only of comparatively recent sub-aerial origin. Much 
of this district 1s practically virgin ground to the geologist, 
lying in West Australa and the Northern Territory. 
(b) Geological. 
15. The beds which chiefly concern us are the Cretaceous. 
and Tertiary. 
16. The accompanying map, kindly prepared for me 
by Mr. L. C. Green, late of the Geological Survey of Queens- 
land, and now the able lecturer on Geology at the Brisbane 
Technical College, shows the he of the Cretaceous and 
Tertiary beds as far as at present known. The Cretaceous 
boundary is pretty exact, over much of the area, but it 
must be remembered that a great deal of this formation 
lies hidden beneath the Tertiary strata. 
17. The main point for our present purpose is that the 
Cretaceous beds cut Australia into two portions—a long, 
narrow, mountainous area on the east, and (if we include 
the area faintly hatched as once covered with Cretaceous 
rocks), a compact area of no great height on the south-west. 
There are also inliers of older rocks, which stood as islands 
in the sea. 
18. Dr. A. R. Wallace saw this clearly, and the map in 
his ‘‘ Island Life,” might almost serve my purpose—my 
map is only truer from including evidence unknown at the 
time our great philosophical naturalist wrote his charming, 
and suggestive work. 
19. For reasons that will appear, I shall call the entire 
area the Australian Archipelago, the eastern land-mass 
Australia Orientalis, the western land-mass Australia 
Vera, and the sea between the two Australias, the Opal Sea. 
20. The whole of these Cretaceous beds are marine, 
and have yielded a rich harvest of fossils. They fall into 
two unconformable series, the Lower and Upper Cretaceous, 
whose sub-divisions and local names do not concern us. 
