202 
Geology of Sydney. 
we see that there are two marine formations in the 
Permo-Carboniferous — the Upper and the Lower 
Marine. The fossils shown on pages 195, 197 and 203, 
are illustrations of some of these marine forms. They 
prove conclusively that sediments two thousand feet 
in thickness were deposited on a subsiding sea-floor. 
Subsidence still continued, but the succeeding beds of 
the Greta coal measures were laid down in fresh water. 
Once again the sea covered these last, and in this sea 
the Upper Marine series slowly grew. Fossil collectors 
can, with very little trouble, procure abundance of the 
marine fossils that characterise the Upper Marine. The 
best collecting grounds are enumerated in Chapter 
xiii. The most notable specimens will be 8pirifers } 
and the beautiful lace-like films of Proioretopora that 
sometimes encrust them. 
The 8p infers are often represented by moulds of 
the interior of the shell, formed by sand or clay which 
filled them, while the substance of the shell itself has 
disappeared. There are no Spirifers living now. 
In some periods of the Palaeozoic age the sea-floor 
must have been actually paved with them. They are 
called Spirifers , or spire-bearers, because a part of 
their processes, somewhat resembling watch-springs, 
was coiled up within the shell. These were used to 
support the thread-like organs covered with cilia. 
To form anything like an adequate idea of the life 
that flourished in the Permo-Carboniferous seas, we 
have only to glance at the fragments preserved in our 
museums. Corals, crinoids and star-fishes were abun- 
