Page:Quarterly Journal of the Geological Society of London, vol. 35.djvu/46

20 20 A. V. HOWJTT ON THE PHYSICAL GEOGRAPHY AND

bably also at the Limestone River, Upper Silurian Limestones with corals (at the former containing " Palceopora ") 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 Icevicostata, Placodermatous fish, and corals perfectly identical with specimens from the European Devonian limestones of the Eifel *.

I 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 Palaeozoic fixed points.

II. Upper Paleozoic. 2. Devonian.

(d) Snowy-River Porphyries. — The immense extent of rock masses, both horizontally and vertically, which have 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 Yictoria, as " Trap or Hypogene," and also under the same classification in the more recent sketch map of Mr. B. 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 I have yet been able to work tbem 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 Eiver on the east and the Buchan Biver on the west have cut down into the granites and the associated sedimentary strata, and left these " Snowy-Biver Porphyries " standing up as a high rugged tableland, some 2000 to 3000 feet in altitude above these rivers.

Prom this tableland streams falling into the Snowy Biver 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 generaUy applicable to other places where I have crossed it, as, for instance, from Panwick to Mountain Creek, or from Buchan to the Bodgers Biver. 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 Bange, so that at Buchan the " Lower Palaeozoic

M'Coy, RG-.S., Professor of Natural Science in the Melbourne University, Government Palaeontologist, &c. &c.

Zoology and Palaeontology of Victoria," Essay No. 7, p. 327.
 * Intercolonial-Exhibition Essays, 1866. Professor M'Coy"On the Kecent