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Geology of Sydney. 
by the western railway being 3,658 feet at Clarence 
Siding. The plateau rises in conspicuous peaks at 
Mount Tom ah 3,276 feet, Mount Wilson, Mount King 
George 3,470 feet, and Mount Hay 3,270 feet. The 
portion of the plateau which has suffered least from 
erosion, with the exception of the peaks just enumerated, 
is the ridge known as the Darling Causeway, which for 
a distance of about thirty miles forms the line of water- 
parting between the tributaries of Cox’s River and of 
the Grose River. The course ot the western railway 
line and of the main western road almost exactly follow 
the trend of this causeway. Westwards the plateau 
terminates in sheer precipices of sandstone, from two 
hundred up to nearly one thousand feet in height, of 
which Hassan’s Walls may be taken as a type. The 
creeks which drain southerly from this water-parting 
into the Cox, and those which flow northerly to join 
the Grose, within a few miles of their sources plunge 
over sandstone precipices, forming waterfalls of which 
Govett’s Leap, Leura Falls, and Wentworth Falls 
may be taken as types. From the bases of these 
waterfalls the creeks find their way among masses of 
densely-wooded talus into more or less wide valleys 
sloping gently eastwards. Traced a few miles further 
east, the rivers formed by the junction of these creeks 
become hemmed in by walls of sandstone, which form 
almost impassable gorges near the spots where the 
rivers break through the monoclinal fold at the eastern 
margin of the plateau.” 1 
1 Address to Roy. Soc., N.S.W., 18yG. 
