Ordovi.cian Rocks. 65 



DaiTiwil forms has been limited to those from one or two outcrops in 

 the Darriwil district. As well preserved specimens are rare, the 

 Darriv.il forms are more difhcult to identify specifically than those 

 of lower liorizons. While it was known that the Darriwil series was 

 characterised by species of ^^ Tetragraptus, Didymograjjtus, Logano- 

 graptus, Diplograjitus, C'lhnocograptus, Glossograptus, Trigono- 

 grapfus, Lmiograjjfus, and others not determined,"! its exact rela- 

 tionship to lower beds had remained obscure and fossils found in 

 other localities had thrown little light on the point. The presence of 

 P. ti/2nts,J. Hall, with LogcmograjJtus and large Z). caduceus at Steig- 

 litz was puzzling2, and an assemblage of Newham forms " suggested 

 the presence of lx)th Darriwil and Castlemaine series. "■5 The 

 country to the west of Castlemaine had never l;een critically exam- 

 ined, and it was known to contain much that was new to the grap- 

 tolite succession. Difficult forms found by officers of the Geological 

 Survey half a century a.go were still undescribed, and the chance 

 of clearing away certain anomalies was deemed possible. It took 

 time to acquaint oneself with these new forms, but having done ,so 

 their order of development soon appeared. It soon became appar- 

 ent that the beds could not be called Upper Castlemaine without 

 altering the meaning of the term, nor for the same reason could 

 they be called Darriwil, without widening the meaning of the term. 

 The beds spread over an area of more than thirty square miles at 

 Castlemaine, probably over a greater area at Macedon and Wood- 

 end, and south of Steiglitz, and occur also at Ingliston, Melton, and 

 probably at other localities, and three zones seem to be recognisable. 



In the Darriwil district all zones seem to be represented, the Upper 

 or typically DarriAvil, on Sutherland's Creek (W.L.S. 1, \ S.), 

 and the lower or Oncograptus zone at Steiglitz. 



In view of this all the beds, as already described, have been in- 

 cluded in an extended series, for which the term Darriwil has been 

 retained, and of which the previously known Darriwil beds form, 

 as already stated, the upper zone. If, therefore, in earlier work 

 " Darriwil " is read as " Upper Darriwil," no confusion Avill arise. 



The vertical distance between the Middle and Upper Darriwil 

 zones should be capable of measurement at Guildford, and they 

 merge into one another through transitional beds. 



No zone above that of Tetragraptiis fnifico-ms has such a distinc- 

 tive and characteristic association of species as these Darriwil 



1 Hall, T. S., Australian Graptolites. Fed. Hbk. of .\ust., B.A.A.S. (1914), p. 291. 



2 Ibid., Reports on Graptolites, II. Rec. Geol. Siirv. Vio., vol. iii., part .3 (1914), p. 290. 



3 Skeats, E. AV., and Summers, H. S., Geol. and Petr. AFacedon District. Bull. Geol. Surv. Vic. 

 24 (1912), p. 41. Quoted from Hall, T. S., Geol. Surv. Vict. Pro?. Rept., IX. (1898), p. 126. 



6 



