232 T. W. E. DAVID AND G. H. HALLIGAN. 
of about 90 feet below high water mark, in sinking by means 
of a caisson at this spot, highly carbonaceous clays, with 
abundant remains of plants, mostly in a fragmental con- 
dition, were found to underlie the sandy shell-bearing 
estuarine beds, of the type commonly met with on the 
bottom of our harbour. This section was examined at the 
time by Mr. H. Stanley Jevons and Professor David, and it 
appeared to them that these loamy muds with plant remains 
were strong evidence of the harbour at the time of their 
formation having its water surface much lower than at 
present. In other words, these loamy beds are evidence 
of recent submergence of Port Jackson to the amount 
probably of 90 feet. Then, too, in sinking the cylinder to 
form a pier of the present Hawkesbury Bridge, on the side 
nearest to Mullet Creek, the trunk of a large tree was 
struck by the shoe of the cylinder, and the cylinder in con- 
sequence was carried so much out of plumb that it had to 
be built up anew from below the level of low tide up to the 
base of the bridge. The horizon, where this timber was 
struck, is about 109 feet below sea level. Obviously this 
is not conclusive evidence of submergence, but is very 
suggestive of the surface of the estuary having been very 
much lower than it is at present at the time when the 
Hawkesbury River was able to roll down in flood time and 
embed in its flood silts these large logs. 
In sinking the shaft for the Stockton Colliery numbers of 
stumps of large trees associated with coarse water-worn 
river gravel and shingle were struck at a depth of about 
160 feet below sea level. Obviously these river gravels 
could have been laid down only under conditions where the 
level of the Hunter River approximated to the present 
level of that gravel; this implies a submergence there of 
150 to 160 feet. A continuation of these gravels has been 
traced to still greater depths at the Anna Bay Bores and at 
the bore recently put down by the Perpetual Trustee 
