But Then Immediately Occurs The Startling Difficulty,
Why Has The Sea Worn Out These Great, Though Circumscribed
Depressions On A Wide Platform, And Left Mere Gorges At The
Openings, Through Which The Whole Vast Amount Of Triturated
Matter Must Have Been Carried Away?
The only light I can
throw upon this enigma, is by remarking that banks of the
most irregular forms appear to be now forming in some seas,
as in parts of the West Indies and in the Red Sea, and that
their sides are exceedingly steep.
Such banks, I have been
led to suppose, have been formed by sediment heaped by
strong currents on an irregular bottom. That in some cases
the sea, instead of spreading out sediment in a uniform sheet,
heaps it round submarine rocks and islands, it is hardly
possible to doubt, after examining the charts of the West
Indies; and that the waves have power to form high and
precipitous cliffs, even in land-locked harbours, I have noticed
in many parts of South America. To apply these ideas to the
sandstone platforms of New South Wales, I imagine that the
strata were heaped by the action of strong currents, and of
the undulations of an open sea, on an irregular bottom; and
that the valley-like spaces thus left unfilled had their steeply
sloping flanks worn into cliffs, during a slow elevation of
the land; the worn-down sandstone being removed, either at
the time when the narrow gorges were cut by the retreating
sea, or subsequently by alluvial action.
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