Page:Quarterly Journal of the Geological Society of London, vol. 35.djvu/52

26 26 A. W. HOWITT ON THE PHYSICAL GEOGRAPHY AND

moved the greater portion of it before the succeeding groups of strata were laid down. Denudation had also probably removed much of the volcanic materials of Wombargo and other localities of the Snowy- River porphyries. I have now to consider those groups of strata, which I believe may be classified as above.

Mr. Selwyn described several groups of strata in North-east Gippsland, in the localities of the Avon, Freestone Creek, Iguana Creek, and Mount T ambo, as provisionally classified as Upper Palaeo- zoic, and he regarded the plant-bearing sandstones and conglome- rates of Mount Tambo as being below the fossiliferous limestones of Bindi, and therefore as " older than the true European Palaeozoic coal-measures "*.

I believe that I shall be able to show that this view of the pro- bable age of the Mount-Tambo beds is untenable, being based on a misconception of the true stratigraphical relations of the Mount- Tambo and Bindi formations. At first sight, however, their posi- tions appear to be such as are indicated by Mr. Selwyn.

The groups of strata which until now have collectively been spoken of as the Avon Sandstones have recently been separated into two divisions — the Avon Sandstones proper, containing Lepidoden- dron australe, M'Coy, and referred to the base of the Carboniferous f, and the Iguana-Creek beds, with Arcliceopteris Boiviiti, M'Coy, Anei- mites iguajiensis, M'Coy, and Cordaites australis, M'Coy +, and re- ferred to the Upper Devonian.

Still further inquiries have enabled me to extend the Iguana-Creek beds northward as far as Tabberabbera, and westward as far as Maximilian Creek, thus confining the Avon Sandstone proper within much narrower limits than formerly. The exact stratigraphical relations of the two groups have not yet been worked out. At present I incline to believe that the passage may be gradual from one to the other, that is, from the Upper Devonian to the Lower Carboniferous, which is not unusual elsewhere.

I now proceed to describe the Upper Devonian strata from the typical locality Iguana Creek, and from which I have named the whole group.

Iguana Creek joins the Mitchell River just within the line where the fringing marine Tertiaries thin out on the older rocks. It is here that the Iguana-Creek beds are seen to dip at a low angle under- neath the Tertiary sands and clays. The base of the series is not here visible, the "Lower Palaeozoic formation" having dipped to- gether with the overlying strata, so that at the place mentioned, and also generally, though not at all places along the same line, it is Delow the water-level of the rivers.

by A. R. C. Selwyn, &c, Intercolonial-Exhibition Essays, 1866, p. 17.
 * " Notes on the Physical Geography, Geology, and Mineralogy of Victoria,"

+ A. E. C. Selwyn, " Notes on the Physical Geography, Geology, and Mineralogy of Victoria," &c, Intercolonial -Exhibition Essays, 1866, p. 15; and ' Proclromus of the Palaeontology of Victoria,' decade i. p. 37, by Frederick M'Coy, F.G.S., Government Palaeontologist, &c.

I ' Report of Progress, Geological Survey of Victoria,' No. 2, p. 72.