• BY H. I. JENSEN, D.SC, 173 



bulwarks in the shape of compact and resisting earth 

 segments, the more pliable rocks being moulded against the 

 resisting object. 



There are, no doubt, cases of surface folding, in which 

 the fold movement is exerted from the land in the direction 

 of the sea, as in Fig. 13 (a), where two earth segments, a rising 

 one, A\ and a subsiding one, Bi, are in contact. At their 

 junction the beds will be in some cases overfolded towards B^; 

 in some places fractured and overthrust faults may develop. 

 This type of earth structure is in evidence at Penrith, in 

 the Blue Mountains, X.S.W., and in the Main Range^ 

 Fassifern district, Q. In ^uch cases, we always have a 

 broken plateau, different parts of which are rising or sub- 

 siding at different rates. 



More usually, we have surface folding conforming 

 to the type illustrated in Fig. 13 (6). A synclinal area under- 

 going expansion B^ is folded up against the hard-resisting 

 Palaeozoic rocks, A^. It is clear that folding of this kind 

 may form either a concave or convex range in the direction 

 of thrust depending on the configuration of the opposing 

 mass. {See Fig. (b), (c) and {d).) 



In my paper on the Geology of the East Moreton and 

 Wide Bay Districts, I presented the view that the folding 

 of the Mesozoic rocks of the D'Aguilar Range and the 

 Blackall Range was caused by pressure from the East. 

 This view I still adhere to, and these ranges have a slight 

 convexity to the East. As shown in Fig. 12, the south spur 

 of Mt. Mee has small cappings of Trias-Jura rocks elevated 

 high above the surface of the coastal plain. The pressure 

 from the East must have been rather deep seated, the 

 surface formations being at the time in a state of tension. 



In discussing the merits of the theories advanced 

 by Hedley, Andrews and others on the direction of pressure, 

 it is the deepseated and not superficial pressures that count, 

 for as already shown, the surface formations of Eastern 

 Australia have throughout Tertiary times been in a state 

 of tension, and plateau uplift has been the main cause 

 of mountain building. Plateau dissection accounts for 

 the curvature of our ranges. 



For this very reason it seems absurd to draw inferences 

 as to the direction of existing and Tertiary pressure dis- 

 tribution from the configuration of existing mountain 



