The Shales. 
109 
or, as geologists express it, on various horizons in the 
sandstones. The thickest beds of shales, however, are 
those that lie above the sandstones forming most of 
the surface of the country from Sydney to Penrith. 
Professor David writes thus of the Wianamatta 
Shales: — “Of this formation, which probably at one time 
covered a considerable area on the Blue Mountains, 
only a small portion is left undenuded. The western- 
most extension of these shales is probably at a point 
about half-way between Linden and F aulconbrid p*e. 
o 
At Springwood the shales attain a thickness of about 
eighty feet, and further eastwards are completely 
denuded at intervals, until the monocline at the top of 
Laps tone Hill is reached. They form a thin capping 
near the top of the monocline and thicken out rapidly 
at its base in the valley of the Nepean. They occupy 
almost the whole of the surface area between Penrith 
and Sydney, and extend northwards at least as far as 
the Kurrajong Heights, and southwards beyond Sutton 
Forest. The Rev. W. B. Clarke estimated their maxi- 
mum thickness at eight hundred feet ; he called them 
Wianamatta Shales, from Wianamatta — the native 
name for South Creek. The junction of these shales 
with the underlying Hawkesbury Sandstone is fre- 
quently marked by contemporaneous erosion. The 
shales are dark grey to bluish-grey at a depth, owing 
to the presence of iron, probably as protoxide, and 
carbonaceous material. Near the surface where they 
have been weathered, they have become bleached 
through the aggregation of the iron into segregation 
