446 T. 8. Hall — Graptolite Roclis, Victoria, Australia. 



Ordovician, have been doubtfull}'^ recorded,' the condition of the 

 specimens rendering specific identification impossible, though I 

 consider the generic character of the fossils sufficiently clear. 



Silurian. 



The Saltwater Eiver, in its course south from the Dividing Range, 

 passes over the boundary between the Ordovician and Silurian 

 formations. The river -valley is cut deeply through the great 

 basaltic plain of Western. Victoria, wliich here reaches almost its 

 eastern limit. As is usual in such gorges, the basaltic detritus 

 deeply masks the hill-sides, and outcrops of older rocks ai'e isolated 

 and small, so that whether the junction is conformable or not has 

 not been settled. The question has been avoided on our geological 

 maps by colouring Ordovician to the border of one sheet and 

 beginning the next with Silurian. In the north-east of the colony, 

 however, at Wombat Creek, there is, according to Mr. W. H. 

 Ferguson, of the Department of Mines, an unconformable junction 

 with a conglomerate at the base of the Silurian. The graptolites 

 from the lower beds which he obtained, and which were submitted 

 to me by the Department, are, as mentioned above, of Ordovician age. 

 The fossils from the upper series over the conglomerate were sent 

 to Mr. R. Etheridge, jun. They were in a very imperfect state, 

 but from an examination of them Mr. Etheridge says ^ that he is 

 " inclined to regard the specimens .... as of Upper Silurian 

 age," Upper Silurian being used in the sense in which Silurian is 

 used in this paper. There would appear from this, then, that there 

 is a physical unconformity between the two formations in Victoria. 

 That an unconfornnty exists was long ago asserted hy Dr. Selwyn,^ 

 the statement being based on the diflerence in the average amount 

 of dip in the two formations, and not on any observed contact. 

 Mr. E. A. F. Murray, lately Government Geologist of the Colony, 

 says that "the precise lines of junction of the two groups have 

 not yet been so nearly ascertained as to enable it to be stated that 

 they are stratigraphically unconformable."* Mr. Ferguson's observa- 

 tions, however, would seem to settle the point. 



As previously mentioned, the earliest known graptolite locality in 

 Australia lies near the township of Keilor, where Aplin found 

 specimens in 1855. There are one or two species of Mouograptidae 

 present, none of which I find well enough preserved for description, 

 and Diplograptas is possibly represented. About a mile from the 

 locality just mentioned another outcrop occurs, which contains a few 

 examples of Monograptus, but which is chiefl}^ noticeable as being 

 the spot where Retiolites Australis, McCoy, is found, and which has 

 not hitherto been found elsewhere. 



The records from other localities are not very satisfactory. I have 

 identified Monograptus priodon, from Macclesfield, and M. cf. diibiiis, 



1 Geol. Surv. Victoria, Prog. Rep., vol. ix (1898), pp. 126-8. 



2 Ibid., p. 126. 



^ Intercolonial Exhibition Essays, Melbourne, 1S67, p. 12. 

 * " Geology and Physical Geography of Victoria," p. 43-. 



