318 THE BONDI ANTICLINE, 



rising witli increased rapidity near Sydney* point to the com- 

 pletion of tlie series by an anticline on the east. It is proposed 

 to name this the Bondi Anticline. Apparently its crest lay 

 beyond the present coast, and though now shattered and sunk, 

 may yet be traced from its dyke-complex, and from the crushing 

 of the rocks before it. 



In its prime, the Bondi anticline probably rose to a consider- 

 able height, for denudation has pared off from its flanks the 

 Wianamatta shale and some sandstone as well. The drowned 

 valley of Port Jackson indicates recent subsidence: so that the 

 anticline sank, perhaps through the withdrawal of a fluid core, 

 perhaps through being involved in another and larger folding 

 movement, or perhaps through faulting. 



Evidence in support of this idea is offered from the radiating 

 dykes and from the crushing of the shale. 



(1) The radial dykes. — Around S3'dney, the sandstone-rocks 

 are fissured by a series of dykes, some of which run roughly 

 north and south, and others cross at about right angles. Both 

 are of later date than the crushing of the shale, as they traverse 

 the distorted strata indifferently. 



It was remarked by Mr. G. A. Waterhouse that the easterly 

 and westerly series assumed a radial direction, and converged 

 to a point east of Bondi. f 



If the Bondi anticline swelled to bursting point and then 

 cracked lengthwise and crosswise, these dykes Avould be the casts 

 of those cracks (Platexxv.). By their direction, the hypothetical 

 anticline might be restored as a crescent billow convex to the 

 present coast and rising in the centre. When pressure was 

 relieved by the bursting of the lava into dykes, the folding move- 

 ment was perhaps arrested. 



(2) The mashing of tlte anticline. — In the composition of the 

 Hawkesbury Sandstone, the Rev. J. E. Tenison- Woods dis- 

 tinguished a smaller stratification, whose lines are mostly in- 

 clined to the horizon, as " laminae," and a greater division, 



* David & Pittman, Journ. Roy. Soc. N. S.Wales, xxvii., 1893(1894), p. 459. 

 t Morrison, Rec. Geo). Survey N.S.W., vii., 1904, p.261. 



