34 T. W. E. DAVID. 
to the eye horizontal ; but they probably have a similar inclination 
‘with the surface of the platform, which slopes from the west 
towards the escarpment over the Nepean, at an angle of one 
degree or of one hundred feet in a mile. The strata of the 
escarpment dip almost conformably with its steeply inclined face, 
and with so much regularity that they appear as if thrown into 
their present position; but on a more careful examination they 
are seen to thicken and to thin out, and in the upper part to be 
succeeded and almost capped by horizontal beds. These appear- 
ances render it probable, that we here see an original escarpment, 
not formed by the sea having eaten back into the strata, but by 
the strata having originally extended only thus far. Those who 
have been in the habit of examining accurate charts of sea coasts, 
where sediment is accumulating, will be aware that the surfaces 
of the banks thus formed, generally slope from the coast very 
gently towards a certain line in the offing, beyond which the 
depth in most cases suddenly becomes great. I may instance the 
geat banks of sediment within the West Indian Archipelago, 
which terminate in submarine slopes, inclined at angles of between 
thirty and forty degrees: every one knows how steep such a slope 
would appear on the land. Banks of this nature, if uplifted, 
would probably have nearly the same external form as the plat- 
form of the Blue Mountains, where it abruptly terminates over 
the Nepean.”? 
It is evident from the above passage, that Darwin regarded the — 
eastern escarpment of the Blue Mountains as an original structure 
in the Blue Mountains, formed, that is, contemporaneously with 
the deposition of the sandstone. 
Darwin states further,’ “The strata of sandstone in the low 
coast country, and likewise on the Blue Mountains, are often 
divided by cross or current laminz, which dip in different direc- 
tions, and frequently at an angle of forty-five degrees.” Speaking 
of the grand valleys of the Blue Mountains, from 1,500 to 2,000 
—_ 
2 Op. cit., pp. 149-150. 3 Op. cit., p. 150. 
: 
a 
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