94 
Geology of Sydney. 
it. The fulgarites are found in the form of irregular 
tubes varying from one-quarter of an inch to three 
inches in diameter. These tubes give off smaller tubes 
as they descend, and are invariably coated on the 
inside with a perfect enamel of fused quartz. With 
a hand lens the enamel is seen to be quite full of vesicles 
evidently due to the conversion of the water that 
was present into steam or perhaps its constituent gases. 
Alluvial. — The low-lying lands anywhere about 
Sydney are recent deposits of alluvium. Better 
examples can be found on the Nepean River from 
Penrith to Richmond. The Richmond Flats and the 
rich plains around Penrith are deposits left by 
rivers, but of course older than the deposits now form- 
ing by the river silting up in places. High floods are 
still adding fresh deposits to these plains down to the 
present day. The material laid down in this way 
supplies a lesson on denudation and the transporting 
power of rivers. Pebbles and boulders of granite, 
quartz, and porphyry can be found in the alluvial 
deposits near Penrith that must have travelled from 
the upper reaches of the Cox River, forty miles or 
more away, as the river runs. 
In the Cliffs at Long Bay a layer of mould, three 
feet below the surface, has been recognised as an old 
land surface. Human remains with some stone imple- 
ments have been found on this old land surface. Stone 
implements were also found in the deposits covering 
the submerged forest at Shea’s Creek. 
