BY H. I. JENSEN, D.SC. 161 



of Jack) an epicontinental sea formed in which the Trias- 

 Jura rocks were laid down. This sea extended from the 

 New England and Central tablelands in New South Wales 

 west into Central Australia, thence north to the Gulf of Car- 

 pentaria. It reached the eastern margin of the present 

 Continent in the Moreton Bay district of Queensland, 

 whence a stretch of water extended south over the Clarence 

 and Richmond districts of New South Wales. 



The Trias-Jura sea is coextensive {Fig. 8) \\ith the 

 artesian areas of New South Wales and Queensland, and 

 included also the Ipswich and Clarence coal-measures. 



The bulk of the sediments deposited in this period 

 consisted of coarse, silicious sandstones, distinguished by 

 current bedding and scarcity of fossils. In parts, as on 

 the Maroochy Beach of Queensland, fossil wood is plentiful. 

 In isolated places leaves and thin-shelled mollusca are 

 found. Evidently, the conditions prevailing in this expanse 

 of water were similar to those prevailing in the Hawkesbury 

 period over the Sydney basin. 



The area subject to sedimentation in the Cretaceous 

 period was almost identical with the Trias-Jura basin. 

 [Fig. 9). 



In the Cretaceous Mediterranean Sea of Australia 

 were deposited the Rolling Downs formations, consisting 

 of sandstones, marls and limestones, with marine fossils. 

 The Cretaceous sea was probably connected with the ocean, 

 both to the south and to the north. 



The Rolling Downs are capped by the Upper Cretaceous 

 or Cretaceo- Tertiary Desert Sandstones, fine-grained, 

 magnesian sandstones — this formation often lies uncon- 

 formably, and occurs in the form of broken ridges with 

 flat summits and precipitous sides. The Rev. Mr. Tennison 

 Woods, F.L.S. [9], considered the Desert Sandstone to be 

 an early Tertiary volcanic tuff deposit, formed under 

 terrestrial conditions, the false bedding being due, in his 

 opinion, to wind changes (Proc. Roy. Soc. of N.S.W., 

 Vol. XXII., p. 290). He considers also, that in the period 

 of the Desert Sandstone, Australia Avas more elevated than 

 to-day. 



The theory of the volcanic origin of the magnesite 

 of the Desert Sandstone is probably correct. Although 

 the main trachytic eruptions of Eastern Australia were 



