22 Transactions. 
thick and continuous series, rests unconformably on the Ordovician slates 
and porphyroids, fragments of which it includes, and is followed by a thick 
that its presence indicates that the orogeny occurred during Upper 
Ordovician time, and the subsequent transgression commenced in the 
Gulf in South Australia may also be part of the same series. According 
to Maitland (1919), we may perhaps group as probably coeval with these 
the almost horizontal unfossiliferous sandstones, dolomitic limestones, &c., 
of the Nullagine series, which, overlying a crystalline complex, cover 
present in the Macdonnell Ranges include the following genera: H yalo- 
stelia, Orthis, I. soarca, Palaearca, Pteronites, Eumena, Raphistoma, Ophileta, 
Orthoceras, and Asaphus. Tate (op. cit.) thought that these indicated a 
the Australian Ordovician neritic forms, for they are not very marked, 
yet the relations of the species seem to be with north European forms. 
It would seem, therefore, as if the late Ordovician orogeny had been 
accompanied by such changes in the geography of the other parts of the 
orld as to open the Australian seas to the stream of European life- 
period, but the sea continued in the eastern States, where a continuous 
succession of Silurian rocks was laid down. 
Silurian. 
th its transitional Ordovician-Silurian 
auna, appears as the oldest of the Silurian fossiliferous formations in 
the eastern States. Among the forms present are Favosites, Tetradium 
(which was at first referred to Archaeocy 
al : 
Dalmanella, Camarotoechia, Pentameru 
athus), Halysites, Pleurodictyum, 
equivalent to the Lower Sil n 
1896 ; » 1910; Chapman, 1919) uran beds are repre 
m 22. В ѕеп 
northern Tasmania by the Chudleigh limest : эне тры E 
(Etheridge, 1898). g Stone, which contains Ha ysite. 
