GEOLOGICAL FAULT AT KUKBAJONG HEIGHTS. 361 



abrupt eastern margin of the Blue Mountains, up which 

 the Great Western Railway Zig-zag ascends at Lapstone 

 Hill, near Emu Plains, marks the line of a similar, though 

 not such an extensive fault, by which all the country 

 between it and the coast was thrown down to its present 

 level — the depression being so great that the ocean water 

 flowed into the old river valleys, one of which forms the 

 beautiful harbour of Port Jackson." A later brief refer- 

 ence is that made by Dr. J. E. Taylor, 1 in which he speaks 

 of " the great Nepean fault." 



In my Presidential Address to this Society in 1896, 2 I 

 stated as the result of my observations in the field that the 

 eastern escarpment of the Blue Mountains above the 

 Nepean, from Lapstone Hill to the Kurrajong, was due to 

 a monoclinal fold rather than to a fault, (op, cit. 63, and 

 diagram 2, of plate n.) 3 On the same diagram it is shown 

 that while the monocline depresses the Triassic Strata 

 fully 400 feet in an easterly direction, there is also present 

 a small fold in the strata about one mile west of the 

 monocline, and passing through Glenbrook Railway Station. 

 This small fold faces the west and displaces the strata in 

 that direction to the extent of about 100 feet. It is possible 

 that this western fold is accompanied by shearing, and it 

 is almost certain that it is a structural feature which is 

 identical with the Kurrajong fault. 



There are thus at Glenbrook two geotectonic structures 

 of importance (1) the eastern monocline of Lapstone Hill, 



1 Our Island Continent — a Naturalist's Holiday in Australia, by Dr. 

 J. E. Taylor, f.l.s., f.g.s., London 1886, pp. 249 - 250. 



2 Journ. Eoy. Soc. N. S. Wales, Vol. xxx., 1896, pp. 33-41. 



3 I should like to take this opportunity of correcting an error made by 

 me in drawing the Section, diagram 1 of Plate n.,op. cit. The "Penrith 

 Bore " is there shown as having been started at the top of the Hawkes- 

 bury Sandstone. The bore is in reality situated at the bottom of a deeply 

 eroded gorge in the Hawkesbury Sandstone, forming the present channel 

 of the Nepean River. The top of the bore is actually about 200 feet 

 below the original top of the Hawkesbury Saudstone. 



