We are therefore driven to some cause inherent in the 

 rocks of the floor ; and I suggest that the rolls are of the 

 nature of expansion " folds " due to the swelling up of the 

 shale as a result of hydration or oxidation or both. It 

 has been shown that the overlying rocks are all somewhat 

 porous so that the access of water carrying oxygen is 

 easily accounted for. A similar effect is very widespread 

 in the Wianamatta Shales of the Sydney area, and the folds 

 are very conspicuous features in almost all the deeper 

 railway cuttings between Sydney and Penrith. In this 

 case we have all stages of development from simple anti- 

 clines, through overfolds, to overthrust faults, but when 



The relationship of any of the rolls to the faults is by no 

 means clear. Both have a common general trend, and are 

 frequently found in association. The faults, so far as I 

 have been able to determine, are always normal and not 

 reversed, as we should expect, if they were due to expansion. 

 They have throws varying from a few inches to upwards of 

 a hundred feet. I am inclined to think the faults antedate 

 the formation of the rolls, and that the fault blocks have 

 formed the resistant blocks against which the shales have 

 been folded subsequently, The superior limit of age of the 

 rolls is indicated by the interesting occurrence, noted on 

 page 383, of a sill being truncated by the compression effect 

 of the roll. The basalt sills are probably Tertiary, hence 

 the rolls must be Pre-Tertiary, and they are probably Post- 

 Triassic. 



In conclusion I wish to express my thanks to all those 

 who have assisted me in the investigation of this interest- 

 ing problem, and especially to Messrs. — Jones, and T. 

 Bissell of Mount Keira, and Messrs. — Sellars and H. L. 

 Garlick of South Bulli. 



