526 NEW SOUTH WALES. 
verse to it. Such cracks might take place without corresponding 
fractures in deposits below, since the Sydney sandstone, besides being 
more brittle, is farther removed from the centre of oscillation. The 
trend of the fissures corresponds with the two great systems of island 
ranges in the Pacific, and of mountain ranges in the world; and they 
afford additional illustration of the great principle in dynamical 
geology, explained on pages 425-436. 
In the preceding pages we have traced out the principal points in 
the geological history of New South Wales, through the system of 
deposits described in the foregoing chapters. We have seen evidence 
that along by the eastern shores, before the coal era, there was a 
muddy bottom abounding in animal life; that ejections of basalt in 
Illawarra, and probably also in some other parts, buried the mud, de- 
stroying all life, silicifying the shells, and hardening the rock as well 
as forming concretions, through the agency of the heated siliceous 
waters; that the region emerged from the sea, and was near the 
water's edge when the coal series began; that the layers of the coal 
series were probably deposited by fresh waters during the different 
states of annual floods, and wider deluges occurring at more distant 
periods ; that a subsidence, which may have been gradual during the 
coal depositions, finally submerged the whole, or brought it to the 
sea level, and then the Sydney sandstone, with its occasional argilla- 
ceous layers, began to accumulate, either along beaches, or more pro- 
bably in water sufficiently shallow for the bottom to be covered by the 
waves. Before the lowest of these deposits, basaltic or greenstone 
rocks were abundant in New South Wales, and during their progress 
similar eruptions occasionally took place, and earthquakes caused 
fissurings of the rocks. From this point we may continue the geolo- 
gical history of New South Wales, by speaking of the degradation 
which has taken place over its surface, and the evidences of recent 
changes of level. 
VIL DEGRADATION OF THE ROCKS OF NEW SOUTH 
WALES AND FORMATION OF VALLEYS. 
The great depth, extent, and number of the valleys of New South 
Wales are calculated to excite wonder, and perplex us much in the 
study of their origin. In some of these sandstone regions, the gorges 
intersect the country in endless succession, and are alike in their inac- 
cessible precipices of one, two, or three thousand feet. ‘They are deep 
