ANNIVERSARY ADDRESS. 35 
feet deep, which terminate at their upper ends in vast amphi- 
theatrical depressions bounded by gigantic walls of sandstone, 
Darwin says, “To attribute these hollows to alluvial action, 
would be preposterous. * * * Some of the inhabitants 
remarked to me, that they never viewed one of these bay-like 
recesses, with the headlands receding on both hands, without being 
struck with their resemblance to a bold sea coast. This is certainly 
the case. * * * But then immediately occurs the startling 
difficulty, why has the sea worn out these great, though circum- 
scribed, depressions on a wide platform, and left mere gorges, 
through which the whole vast amount of triturated matter must 
have been carried away? The only light I can throw on this 
enigma, is by showing that banks appear to be forming in some 
seas of the most irregular forms, and that the sides of such banks 
are so steep (as before stated) that a comparatively small amount 
of subsequent erosion would form them into cliffs ; that the waves 
have power to form high and precipitous cliffs, even in land-locked 
harbours, I have observed in many parts of South America. * * 
To apply these ideas to the sandstone platforms of New South 
Wales, Iimagine that the strata might have been heaped on an 
irregular bottom by the action of strong currents, and of the 
undulations of an open sea: and that the valley like spaces thus 
left unfilled, might during a slow elevation of the land, have had 
their steeply sloping flanks worn into cliffs ; the worn down sand- 
stone being removed, either at the time when the narrow gorges 
were cut by the retreating sea, or subsequently by alluvial action.”® 
It is equally clear from the passages above quoted, that Darwin 
regarded the valleys of the Blue Mountains like the eastern 
escarpment, as original depressed areas in the region of sedimen- 
tation at the time when the sandstones of the Blue Mountains 
were being deposited. Later observers favoured, by far better 
sections than those to which Darwin had access, have collected 
evidence which proves that Darwin’s views, for reasons which 
will be adduced presently, must now be considerably modified. 
1 Op. cit., p. 153. 2 Op. cit., p. 154. 
