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Geology of Sydney. 
“ In the railway sections between Penrith and 
Sydney the shales exhibit folding and faulting on a 
small scale, due, I think, rather to an expansion of the 
shales through weathering than to deep-seated dis- 
turbances. This is proved by the fact that these 
folds and faults may be observed to completely 
disappear downwards as they approach the surface of 
the underlying Hawkesbury Sandstone ; they are, in 
fact, what may be termed expansion folds and 
expansion faults. In their upper portions the Wiana- 
matta Shales become arenaceous, and towards Mitta- 
gong assume a chocolate or reddish purple colour, 
which makes them (in hand specimens) almost in- 
distinguishable from the chocolate shales of the 
Narrabeen Beds. Barytes occurs in these shales as 
well as in the Hawkesbury Sandstone .” 1 
From Sydney to Penrith we have the coastal 
plain, on which the Wianamatta Shales can be seen 
almost anywhere. Wells and road-cuttings show 
good sections of these shales, in which fossil plants 
are abundant. Ferns, especially, are plentiful. Some 
wells and shafts at Blacktown have cut through seams 
of coal ten to twelve inches thick. At Penrith we 
enter the region that has rendered the Blue Mountains 
famous. We are on the eastern boundary of the 
great plateau of Hawkesbury Sandstone, standing 
from one to three thousand feet above sea level. 
This plateau is scored by deep and often narrow 
gorges, cutting down through the sandstone and the 
X David: Anniversary Address. Royal Society, N.S.W. i896. 
