BY H. I. JENSEN, D.SC. 169 



general uplift, and so pinched in between two other blocks, 

 and when the area is underlying mountain building by 

 igneous injection. 



Thus the elevated Triassic Hawkesburj^ sandstones 

 of New South Wales are not superficially folded, nor are 

 the Pernio- Carboniferous sandstones of the Shoalhaven 

 district (Kowra Grits). There have been no abyssal 

 injections of magnitude introduced into them since their 

 deposition. They have never been intruded by granites 

 or diorites, or gabbros. This is also true for the Ipswich 

 Coal Measures in Southern Queensland. 



But the Ipswich Coal Measures are locally disturbed 

 to a considerable degree at Ipswich in proximity to a fault 

 which suggests that this jjortion of the area is a Senkungs- 

 feidt. They are also slightly folded in the D'Aguilar Range, 

 near the Glass House Mountains, the uplift here having 

 probably igneous injection as the immediate causal agent. 



Those portions of a continental margin which have 

 their cracks and maculse infilled by magmas creeping 

 along the zone of flowage became cemented together, and 

 persist as land for many periods, while those portions which 

 are not affected by igneous injections are weakened and 

 tend to become downfaulted areas (Senkungsfeldter). 



In illustration of this statement, it might be pointed 

 out that the Kosciusko fault block, the Central Tableland, 

 and the Northern Tableland in N.S.W., abound in huge 

 granitic intrusions, as is also the case with the Stanley 

 River block of South Queensland (Woodford Peneplain). 



In his presidential address to the Linnean Society 

 this year, Mr. C. Hedley gave further particulars of his 

 view that the Tasman deep is a pressure trough, and 

 endeavoured to show that the physiographic features of 

 New South Wales are due to a pressure emanating from 

 the Tasman deep [19 and 20]. 



There is no doubt about the existence of a great fold 

 in the Mesozoic rocks of this part of Australia. The 

 Hawkesbury sandstones and the Nowra Grits have in general 

 a gentle dip towards the sea, and the Peneplains formed 

 by the truncation of the original fold in middle Tertiary 

 times have their eastern margins depressed beneath the 

 sea by a further accentuation of the fold movement. 



