RECENT SUBMERGENCE OF COAST AT NARRABEEN. 235 
‘‘Such forms as Balanus and Ostrea indicate rocky ground 
within a short distance. Nassa, Pyrazus and Cantharidus 
are Suggestive of a mangrove swamp dry at low tide. 
‘nese might, however, be washed thence down to the bed 
of the stream. SolI would prefer to dwell on the evidence 
of Spisula and Choclodesma, and consider that at the period 
of deposition the horizon of these shells was the bed of a 
muddy estuary about 15 to 20 feet deep. Nothing of the 
ocean beach fauna appears. ‘The fossils point decisively to 
the fact that the sea had not free access to the spot. If, 
when the 50 feet horizon was deposited, the land had stood 
higher than the sea, obviously the shells would have been 
fluviatile or terrestrial, not the mangrove fauna produced. 
On the contrary, if then the land stood as low or lower 
than it does now, and if the sea had free access to the spot, 
another fauna would have prevailed there. Conclusion, 
the environment of these specimens was exactly the con- 
dition of the present Narrabeen Creek. An hypothesis, 
that the creek maintained its level relative to the sea, by 
raising its bed with sediment and so balancing subsidence 
"against accumulation, would agree with the condition and 
position of these shells.”’ 
In regard to the roots of trees and other fragments of 
fossil wood, many of these were found to be distinctly 
charred, probably as the result of a bush fire. Certainly 
the conversion into charcoal is not due to ordinary decom- 
position, such as brings about the conversion of wood into 
lignite. Some of the fragments recovered by us from the 
bore were a couple of inches in thickness, and 4 to 5 inches 
long. This wood having been sectioned for microscopic 
examination, Mr. J. H. Maiden, Director of the Botanic 
. Gardens, was good enough to examine the sections, and he 
reported that on examination he could not detect the 
medullary rays characteristic of the Proteacez or Casuarina 
