' GEOLOGY OF NORTH GIPPSLAND, VICTORIA. 19 
of that of the granites; but the localities are, generally speaking, 
between the Tambo and Snowy Rivers, and extending between 
similar limits north of the Great Dividing Range. The granite, on 
the contrary, is found in all places where denudation has been 
sufficiently deep. Where I have been able to examine the contact 
of the quartz-porphyries and the Silurian strata, as at the Omeo 
Plains, 1 have found the latter broken up and penetrated by dykes 
of felstone—which is in places granular (apparently owing to decom- 
position), in other instances, however, compact, and in such cases, 
almost without exception, more or less distinctly quartziferous. 
The forms of Silurian rocks which I have observed to have been 
invaded by the quartz-porphyries are the argillaceous schists and 
quartzites of the Omeo Plains, and the indurated slates and sand- 
stones of Bindi; and we thus see that the irruption of the quartz- 
porphyries has been subsequent to the invasion and alteration of the 
Silurian strata by the granites. Near Bairnsdale the Silurian has 
been broken through by enormous masses of quartz-porphyry and 
allied rocks, which now are seen as the triad group of hills, Mount 
Taylor, Mount Lookout, and Mount Alfred; and here the sedi- 
mentary rocks have either apparently undergone no change, as at 
Bulumwaal, or, as at Clifton, have been altered to very nearly the 
true Hornfels condition. In the river-gravels derived from the 
neighbourhood of those hills fragments of perfect Hornfels are 
frequent, showing that the change has been a common one there. 
Where I have been able to observe the relations of the quartz- 
porphyries and the granites, as at the Snowy River near Turnback, 
and not far from where the latter rocks have invaded the black 
graptolite slates of Deddick, I have found that the quartz-porphyries 
have come up through the granite in mountain masses and with a 
well-defined line of contact. The boundary of the two rocks at 
Turnback seems to be along a north and south line, and may 
indicate a great fault; if so, it is almost the only fault which I have 
been, so far, able to recognize. 
At Turnback we again see the same general relations of the 
Silurian, the granite, and the quartz-porphyries that I have already 
pointed out as being indicated at Omeo Plains, 
All these divisions—the Silurian, the granites, the quartz-por- 
phyries—may from one point of view be regarded as forming a 
group in the geological series. In this aspect they constitute the 
great ‘ rock-foundation ” of North Gippsland on which the younger 
formations rest. 
I find all over the district that this group has been subject to 
enormous denudation during Paleozoic time, and that, broadly 
viewed, the first great stratigraphical break may be placed here. The 
Sections figs. 1 and 2 (pp. 6 & 12) will further illustrate my views on 
this subject. This first ‘‘ Horizon” may be also regarded as marking 
the division between the Lower and Upper Paleozoic times. Below 
it we have, as at Deddick, Lower Silurian slates with Diplograpsus 
rectangularis, M‘Coy*, as the oldest; and at Gibbo River, and pro- 
* *Prodromus of the Paleontology of Victoria, deggde i. p. 11. Frederick 
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