82 
Geology of Sydney. 
history can be made out. The parts absent from one 
volume will be found present in another. Just in the 
same way — although nowhere on earth are the whole 
chapters of the geological record present in a continued 
succession — we can, by comparing the succession shown 
in various parts of the world, construct one complete 
record. Strata are missing here and there, but the 
order of the chapters does not vary in the great stone 
book of Nature. In Fig. 22 we have a sequence 
of the stratified rocks, with some of the best known of 
our formations, placed in their true position. 
At Burragorang, Permo-Carboniferous rocks are 
found resting directly on Granite ; the Devonian, 
Silurian, and Cambrian being absent. 
Around Sydney, Triassic rocks form the surface 
of the country, and representatives of the Jurassic, 
Cretaceous and Tertiary periods, which should be 
present to complete the series upwards, are absent. 
Near Wilcannia, Cretaceous rocks rest directly on 
Devonian sandstones, Jurassic, Triassic, Permian and 
Carboniferous being all absent. The succession, how- 
ever, never varies, and having decided this order or 
succession, we divide the whole series of Stratified 
rocks into three great groups. 
As each great group has fossils peculiar to itself, we 
are thus enabled to recognize identical formations, 
even when they are many miles apart. We can do this 
by observing the similarity of the contained fossils. 
As an illustration, it may be safely said that if a 
geologist discovers the fossil fern shown in Fig. 40, he 
