Palaeozoic Geology of Victoria. 133 



The existing geological map of Victoria shows a striking restric- 

 rtion of Lower Ordovician rocks to a region lying to the west of a 

 line approximating to the meridian of Melbourne, which would sug- 

 gest an important contraction of the sea at the close of Cambrian 

 times. Later investigations, however, indicate that this is more 

 apparent than real. 



Prof. Skeats (40) has shown that a large area in the Mornington 

 Peninsula, originally regarded as Silurian, must now be included 

 in the Lower Ordovician. 



Several inliers of Lower Ordo^^-ician rocks are now known in the 

 Jieart of the Silurian region as far east as the Mansfield district, 

 approximately ninety miles to the east of the Melbourne meridian, 

 and as very large tracts of the mountainous country in the eastern 

 highlands of Victoria are very imj^erfectly explored geologically, it 

 is probable that other occurrences may be revealed in the future. 

 It is unsafe, therefore, in the light of our imperfect knowledge to 

 generalise too positively on the distribution of land and water in 

 early/ Palaeozoic times. Li general, however, it would appear that 

 there was a progressive restriction of the marine basin through 

 Lower Palaeozoic to the close of Silurian. 



In the sections therefore (Diagram. 11), the relative position and 

 extent of the successive basins are merely represented tentatively, 

 summarising our existing knowledge of the palaeogeography of this 

 Ttegion. 



In Upper Ordovician times a marked narrowing of the PaUi.eo- 

 zoic basin appears to have taken jilace, for no Upper Ordovician 

 rocks have yet been found to the west of the Melbourne meridian. 

 'The sea may have then occupied tw'o basins partly separated by the 

 Omeo crystalline belt. (Diagram, 11, Fig. 3.) 



The next event was again a considerable restriction of marine 

 •area, di-'awing the Silurian Sea into a central basin corresponding 

 to the western part of the Upper Ordovician Sea. It is not clear 

 whether complete land conditions intervened before the Silurian 

 Sea reoccupied the site of the western portion of that of the Upper 

 'Ordovician. The evidence of uncoformability is not conclusive 

 everywhere. (Diagram 11, Fig. 4.) The advent of LoAver Devonian 

 "times was marked by the disappearance of marine conditions alto- 

 gether, and the outbreak of extensive terrestrial volcanic activitv, 

 accompanied also by widespread plutonic disturbances and eartli 

 movements. The dacites. porphyrites, granodiorites, and " Snowv 

 River Series," and possibly also the normal granites belong to this 



