Palaeozoic Geology of Victoria. 131 



shown that the Mansfield-Wellington belt has had a particularly- 

 varied history, and it contrasts strongly with the belt to the east, 

 which is almost entirely Upper Ordovician, and which we may call 

 the Dargo-Ovens zone. To the west, on the other hand, the 

 rocks are chiefly Silurian, overlying Upper Ordovician. With 

 regard to the eastern limits of this area, it is perhaps significant 

 that it corresponds closely with the Cambrian outcrop in the Wel- 

 lington district, and also the Howqua-Mansfield and Dookie locali- 

 ties farther north, in the vicinity of which rocks doubtfully re- 

 ferred to as the Heathcotian Series occur; while on the western side 

 forming the boundary in part, between a Lower Ordovician region 

 to the west, there is the important Mt. William-Colbinabbin line 

 of Heathcotian rocks. These boundaries, or geological frontiers, 

 may, therefore, represent certain critical lines in the past earth 

 history, along which tlie struggle for mastery between conflicting 

 earth forces has been repeatedly renewed and fought out. 



Siiccessire Distribution of Land and Water. 



In considering the probable distribution of land and water 

 throughout Palaeozoic times, we can only be guided by the known 

 outcrops of the various formations, and fresh discoveries at any 

 time are liable to modify our views, but the sub-parallel arrange- 

 ment and the restriction of particular formations to certain belts 

 or areas strongly suggest a successive alternation of land and 

 water, which might be brought about by a long continued progres- 

 sive wave-like undulation of the earth's crust. 



If we consider a succession of east and west sections through Vic- 

 toria during the Palaeozoic history, representing them diagram- 

 matically to show the relative position of land and water, certain 

 interesting features are brought out. (Diagram No. 11.) 



With regard to the Cambrian times, our knowledge is far too 

 fragmentary to enable us to form any reliable conception of the area 

 of the sea of that period, but the pre-Cambrian rocks of Western 

 Victoria may have formed the western limit, while on the east it 

 may have been the belt of crystalline rocks of th^ Omeo zone, though 

 there is some doubt as to whether these rocks are really Archaean 

 or altered Ordovician. 



At any rate, a probable view that seems reasonable would repre- 

 sent a Avide Cambrian sea, occupying the greater part of the now 

 dry land of Victoria, with ancient land masses in the east and the 

 west (Diagram No. 11, Fig. 1). 



Practically all the Cambrian rocks of Victoria «o far known repre- 

 sent accumulations of submarine volcanic material of the nature of 



6 



