20 A. W. HOWITT ON THE PHYSICAL GEOGRAPHY AND 
bably also at the Limestone River, Upper Silurian Limestones with 
corals (at the former containing ‘“‘ Pulwopora”) as the youngest 
known strata. 
Above this ‘‘ Horizon” the first sedimentary deposits known to 
exist, and in places immediately resting on the “ rock-foundation,” 
are Middle Devonian marine limestones, with Spirifera levicostata, 
Placodermatous fish, and corals perfectly identical with specimens 
from the European Devonian limestones of the Eifel *. 
IT shall in the next division of this paper refer to these ; but before 
. doing so I must discuss an extensive formation which lies between 
those two Paleozoic fixed points. 
Il. Urrern Patozorc. 
2, Devonian. 
(d) Snowy-River Porphyries—The immense extent of rock 
masses, both horizontally and vertically, which haye been known by 
the above designation have, so far, included nearly all the rocks oc- 
curring over the tract coloured by Mr. Selwyn, in his geological 
sketch map of Victoria, as ‘“‘ Trap or Hypogene,” and also under the 
same classification in the more recent sketch map of Mr. R. Brough 
Smyth, the present Director of the Survey. The greater part of this 
area is occupied by porphyritic rocks of the acid series and by 
granites. Of the former, some are the quartz-porphyries which I 
have already considered. The remainder are, so far as { haye yet 
been able to work them out, immense accumulations of ancient vol- 
canic materials, consisting principally of ash and agglomerates and 
of felstone lavas. 
One tract only I have as yet been able to examine in any but a 
cursory manner. The country is rugged in the extreme. The Snowy 
River on the east and the Buchan River on the west have cut down 
into the granites and the associated sedimentary strata, and left these 
“« Snowy-River Porphyries” standing up as a high rugged tableland, 
some 2000 to 3000 feet in altitude above these rivers. 
_ From this tableland streams falling into the Snowy River and 
the Buchan (or Native-Dog Creek) have cut deep clefts, among whose 
rugged defiles the geologist can only make his examinations with 
great difficulty and not altogether without danger. 
The subjoined diagram section (fig. 6) across this tableland will 
illustrate my views of its structure, and is also generally applicable to 
other places where I have crossed it, as, for instance, from Fanwick 
to Mountain Creek, or from Buchan to the Rodgers River. ‘The 
natural features have been condensed, and the horizontal distance 
much shortened, in order to bring the whole under view. The dip 
of the country generally seems to be towards the sea-coast from the 
Great Dividing Range, so that at Buchan the “ Lower Paleozoic 
M‘Coy, F.G.S., Professor of Natural Science in the Melbourne University, 
Government Palzontologist, &e. &e. 
* Intercolonial-Exhibition Essays, 1866. Professor M‘Coy “On the Recent 
Zoology and Palzontology of Victoria,’ Essay No. 7, p. 327. 
