Palaeozoic Geology of Victoria, 85 



Dicranograptus nicholsoni, Hopkinson. 

 Dicranograptus hians, T. S. Hall. 

 Nemagraptus gracilis, J. Hall. 

 Lasiograptus margaritatus, T. S. Hall. 



Most of the above species are widespread and abundant in their 

 occurrence throughout the area, but Orthograptus calcaratus has 

 only been found at one spot in the north-western extremity of the 

 Ordovician, marked G, where it is associated with abundant Clima- 

 <;ograptus bicornis and another rare form, C. tridentatus. The 

 last-named species was also found at another locality, marked G.^. 



Splendidly preserved specimens were obtained, and it is the first 

 undoubted record for Victoria, a doubtful instance has been re- 

 Kjorded from Cravensville. 



Nemagraptus gracilis has only been found in Roan Horse Gully. 



Dicellograptus gurleyi is also rare, and has only been recorded 

 irom the Wellington area. 



See comparative table, showing general record of Ordovician 

 graptolites in Victoria. 



It is interesting to note that a sanall amount of turquoise wa« 

 observed in several places, chiefly as very thin veinlets in the joints 

 of the cherty rocks and, occasionally, also associated with white 

 quartz. 



The mineral is evidently widespread in its occurrence in the 

 Upper Ordovician rocks in Victoria. The best known localities are 

 Ryan's Creek, Myrrhee (31), and Mt. Avis, Edi, King Valley, 

 Mr. Caldwell tells me that he found it in black slate on the Black 

 River, and I found it myself in light-coloured chert in the Tara 

 Range. 



A certain amount of white powdery phosphatic material also 

 occurs irregularly distributed along joints and fractures. One 

 sample of altered siliceous rock yielded an analysis 8% of P2O5. 



Some phosphatic deposits of promise from an economic stand- 

 point occur in the vicinity of Mansfield. They are associated with 

 Ordovician rocks, but their true relation is still the subject of con- 

 troversy. 



The cherty nature of the Ordovician rocks of the Wellington 

 -district is a noteworthy feature. Ihe prevailing colour is black, 

 and the most completely altered bands are of the nature of lydianite 

 or black jasper. All grades of silicification occur, and thougli in 

 general the clierts run in bands with intervening l)elts of more 

 normal slate, instances are common showing slightly chertified slate 



SA 



