532 & NEW SOUTH WALES. 
whenever they become thus flat-bottomed, they contribute to its late- 
ral enlargement. At the same time, the bluffs at the lower extremity 
or embouchure of the main valley remain without much change, as 
the denudation is mostly confined to the vicinity of the streamlets 
alluded to, and these streamlets are most abundant above, since they 
are produced and fed mostly by the rains in the higher part of the 
mountains. It is natural enough, therefore, that the valleys should 
not only become flat below and precipitous in their sides, but also that 
they should widen least at their lower extremity. We see, therefore, 
no necessity of appealing to any other cause than simply running 
water, to account for the most stupendous results in Australia. 
It has been supposed that the sea has been largely concerned in the 
denudation which has produced the Australian valleys. On this point 
enough, perhaps, has already been said on a former page. We find 
no reason for attributing any of the valleys to this source, although 
it is possible that some modifications may thus have resulted. The 
facts at Port Jackson are a sufficient reply on this point. The cliffs 
of the estuary actually undergo very little change from the action of 
its waters, and are far more altered by the mode of efflorescence de- 
scribed, and by rills of running water ; and such action as is exerted, 
tends to remove the headlands instead of deepening the coves. ‘There 
is, therefore, good reason for believing that such estuaries as Port 
Jackson and Macquarie were dug out by fresh waters, and have since 
been submerged. The fact that there is a correspondence in trend 
with the fissures of the sandstone, shows that their direction was de- 
termined by these fissures, or by faults which have the same origin. 
We have remarked that the rock has not the same dip in the two 
Heads of Port Jackson, a fact indicating the existence of one or more 
intermediate faults. 
Action of the Sea.—The proper action of the sea is seen in the cha- 
racter of the sandstone shores of Kast Australia, and especially in the 
wide platform of rock, below high tide level, lying at the foot of lofty 
cliffs. ‘The manner in which the shore rocks are worn so as to leave 
this wide platform, has been explained on page 109. It is a simple 
projection of the lower layer of the cliff; from above it, the waves 
have carried away the rock to a distance inward of fifty to one hun- 
dred and fifty yards. A view of this platform is given in the sketch 
of the South Head of Port Jackson. It occurs, with few interruptions, 
along the whole range of sandstone shores. At Newcastle, also, and 
_ Wollongong Point, are fine exhibitions of it. ‘The rock is so fragile 
