360 T. W. E. DAVID. 



the Nepean," marked the original termination of a great 

 bank of sediment, like those "within the West Indian 

 Archipelago, which terminate in submarine slopes inclined 

 at angles of between thirty and forty degrees." Later 

 observers, however, favoured by better sections than those 

 to which Darwin had access, have shown that this escarp- 

 ment was not an original feature, but that it has been 

 superinduced upon the strata, long subsequent to the time 

 of their deposition, by earth-movement. Mr. J. E. Oarne, 

 f.g.s., has drawn my attention to the following reference 

 to the monocline by the late Rev. W. B. Clarke : — "Along 

 the Nepean, where the escarpment of the Blue Mountains 

 forms the side of a great fault, the Wianamatta beds abut 

 against the Hawkesbury rocks, or recline at a high angle 

 on the slopes, proving there a distinct difference in time 

 of deposit." 



The next reference noted by me is that by the Rev. 

 J. E. Tenison-Woods. 2 He states, (op. cit., p. 55) " There 

 are, however, at the first Zig-zag very many signs of a 

 downcast or fault. There the beds are for a very short 

 distance highly inclined against the range, having the 

 appearance of an immense landslip from the failure or sub- 

 sidence of the ground. The rock which is inclined appears 

 to be bent down from the main mass which is quite hori- 

 zontal." In discussing Mr. Tenison-Woods' paper, Mr. O. 

 S. Wilkinson said (op. cit. p. 93), " It has always been the 

 opinion of geologists that there has been a subsidence of 

 the area between the sea and the base of the ranges near 

 the Nepean, as stated by Mr. Tenison-Woods." 



Mr. C. S. Wilkinson, the late Government Geologist of 

 N. S. Wales, also referred to this structure. 3 He says, "The 



1 Catalogue Nat. and Indust. Products, N. S. Wales, 1871, p. 520. 



2 "The Hawkesbury Sandstone," by the Eev. J. E. Teuison- Woods, 

 f.g.s., f.l.s. — Journ. Roy. Soc. N. S. Wales, Vol. xvi., read May 20th, 

 1882, pp. 53-116. 



3 Mineral Products of N. S. Wales, 1882, p. 52. 



