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ANNIVERSARY ADDRESS. 65 
marked concavity in the trough of the fold which appears to me 
to point to a positive downward movement of this part of the 
earth’s crust with regard to sea level. The evidence for a sub- 
mergence, in Tertiary or Post-Tertiary time, of the coastal strip 
is strong, though it is just possible that this may have been due 
to a rise in the level of the ocean consequent on the removal of 
the great ice-sheets of the northern hemisphere at the close of the 
glacial epoch. The fact is worthy of notice, that the trend of 
the fold is not at right angles to the greatest diameter of the area 
of sedimentation, as one would have expected to have been the 
case had the fold resulted from expansion due to the rise of the 
isogeotherms. The movement was probably connected with the 
widespread one which determined the outline of the Australian 
coast in Tertiary time. (See Plate 4.) 
D. Sculpture. Sufficient evidence has already been adduced 
to prove that the valleys of the Blue Mountains have been formed 
through sub-aerial erosion, and do not owe their shapes or positions 
to any original depressions in the sheets of sediment out of which 
they were formed, or to marine erosion. Had the sea played any 
part in their erosion there could not fail to have been some traces 
left behind of raised beaches: no vestige of such have as yet been 
discovered in the Blue Mountain area. As already noticed by 
Darwin, the valleys are somewhat funnel-shaped, being wider 
westwards and narrowed eastwards to deep gorges with precipitous 
sides. This structure is related to that of the geological mor- 
phology of the region. In the westward portion of the Blue 
Mountains the soft strata of the coal-measures which underlie the 
sandstones of the Hawkesbury series stand high, and have thus 
been much exposed to denudation, and have led to a constant 
undermining of the sandstones wherever these softer rocks have 
been brought within reach of denuding agencies. As, however, 
the soft strata of the Permo-Carboniferous coal-measures dip east- 
wards at a more rapid angle than the river channels, which also 
flow eastwards, it follows. that in the east portion of the Blue 
Mountains the rivers leave the strata of the coal-measures and flow 
E—May 20, 1896. 
