204 
Geology of Sydney. 
around the great Permo-Carboniferous depression, — at 
one time a morass clothed in verdure and again a sea 
swarming with marine life. It was from these hills 
that the swollen rivers brought down the sediments. 
“ There was once a splendid city in Egypt, known 
as Memphis. A learned Arab of the Middle Ages has 
told us of its glories. Now all is gone save pyramids 
and sphinx. But it lives again in another place; its 
stones once more shelter human beings ; for out of its 
ruins the modern city of Cairo has been built. This 
use of old building material is one of Nature’s devices 
too. Like the Memphis stones living again with the 
Arabs, our Palaeozoic rocks lived again with new forms 
of life. This is the old story oft repeated in earth- 
history. Silurian grits and slates are probably 
Archaean granites, etc., built up in new ways. From 
these asr&in some of the Carboniferous and Devonian 
rocks were derived ; and again, the rocks we are about 
to consider must have been in part derived from Carboni- 
i'emus and Old Red Sandstone rocks exposed to atmo- 
spheric decay. Thus we read the same cycle of change 
over and over again. The lofty Alpine peak which 
seems so immovable and indestructible must as surely 
be borne down to the sea where it was formed as 
the rain-clouds of heaven must find their way back 
to earth and sea from whence they came .” 1 
“ The hills are shadows, and they flow 
From form to form, and nothing stands ; 
They melt like mists, the solid lands, 
Like clouds they shape themselves and go.” 
1 Hutchinson. “The Autobiography of the Earth.” 
