110 
Geology of Sydney. 
veins and nodules of haematite and limonite, and the 
removal of some of the carbonaceous material. Bands 
and nodules of clay ironstone occur on certain horizons, 
especially near the base of the series, and thin seams 
of coal have been described in the upper beds of these 
shales. Mr. Clarke states that one of these seams 
with its clay bands, at South Creek, has an aggregate 
thickness of four feet.” 1 
The promising appearance of some of the coal 
referred to, when seen in hand-specimens, has sometimes 
led to the belief that these beds belong to the true 
Coal Measures — a very obvious mistake which was 
more than once pointed out by geologists long before 
the Cremorne bore proved that the true Coal Measures 
are quite three thousand feet deeper down. 
Origin of the Sandstones and Shales. 
With one notable exception, geologists are agreed 
in the opinion that the Hawkesbury Sandstones are a 
sedimentary formation. It is not, however, quite 
obvious whether the sandstones were deposited under 
marine conditions, in brackish water, or in fresh 
water. Of course, we look to the fossils to settle this 
point, although it is questionable whether we have 
sufficient material at our disposal to make a final 
judgment. New fossils may be discovered any day 
that would settle the question. The fossils at present 
I Address to Boy Soo., X.S.W., 1896. 
