58 T. W. E. DAVID. 



Shelf off Breaksea Spit at the north end of Fraser Island, 

 is probably due, in the opinion of Captain Sharp and myself , 

 to excavation of the sea floor by a powerful marine current. 

 The chart published by Mr. Hedley (op. cit. p. 18) shows 

 that the bottom has deepened between the years 1870 and 

 1904, by no less an amount than 200 fathoms. As far as I 

 am aware no earthquake shocks have been recorded from 

 this region. This makes it improbable that the change of 

 depth is due to bodily crustal re-adjustment. On the other 

 hand the earthquake shocks which from time to time visit 

 the Adelaide region, the Bass Strait area and the Kosciusko 

 area show that adjustment of the earth's crust is still going 

 on at those localities. Recent observations by the Rev. 

 E. F. Pigot, s.J., etc., at Riverview T Observatory, Sydney, 

 show that the chief earthquake shocks to which the east 

 coast of Australia is subject, come from deeps in the 

 Tasman Sea, such as Carpenter's Deep and Thomson's Deep. 



Conclusions. — The following deductions from the study 

 of the structure of the Australian Continent are only ten- 

 tative : — 1. That Australia, in late Cainozoic time, was 

 larger than at present. It has lost in area peripherally 

 through collapse of marginal segments under gravitational 

 pull. 



2. That orogenic movement has affected Australia up to 

 near the end of the Palaeozoic Era. 



3. That this orogenic movement took the form largely 

 of S-shaped spirals, indicating a tendency of the earth's 

 crust to fold itself in two directions making a wide angle 

 with one another. The dominant direction of the fold lines 

 seems to be about N. by W. to N.N.W., with a tendency on 

 the whole to an overfolding to the west. These meet, 

 mostly in ' syntaxis,' in places in 'linking,' other trend lines 

 directed more E. and W. This spiral arrangement of the 

 trend lines cannot reasonably be correlated with the shape 



