Page:Quarterly Journal of the Geological Society of London, vol. 35.djvu/51

Rh GEOLOGY OF NORTH GIPPSLAND, VICTORIA.

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westward, wherever the nearly vertical strata have been laid hare by denudation and erosion, these strata, shales, and quartzites re- semble those of Tabberabbera more than any others in the district, and of these they are apparently an extension. Such rocks are to be seen at Cobbannah Creek, at Davy's Nob, and thence through to Maximilian Creek, where they constitute the " bed rock " of the gold-workings.

The subjoined section (fig. 8) will convey an idea of the position of the Tabberabbera shales, and is also applicable in its general features throughout the localities which I have just named.

Fig. 8. — Diagram Section across the Mitchell River near Tabberabbera.

S.W. Mitchell River. N.E,

a. Tabberabbera Shales (Middle Devonian).

b. Iguana-Creek beds (Upper Devonian).

c. Felstone sheet.

The Tabberabbera shales have been greatly disturbed and pierced by dykes and masses both of basic and acidic igneous rocks. The former are probably doleritic or basaltic, and the latter porphyritic and quartziferous felstones.

One peculiarity in regard to the position of the Tabberabbera shales deserves mention. The Lower Palaeozoic rocks in most places constitute the " foundation " on which the Upper Palaeozoic strata have been laid down ; but here we find that the Tabberabbera shales have, together with all older formations, been folded, compressed, and denuded ; and on the surface thus formed the nearly horizontal Upper Devonian beds are found to rest. We have therefore the second great stratigraphical break, or horizon, between the Middle and Upper Devonian formations. Although the distinction between the amount of disturbance by which the strata above and below this plane have been affected is more marked than the analogous difference of disturbance above and below the First Stratigraphical Horizon, yet I think that this is due merely to the fact that in descending in time we find that each successive group of rock-formations has been subjected to a cumulative series of disturbing forces.

00 Upper Devonian. — The various isolated groups of strata which have been referred to the Middle Devonian period appear to be merely the remains of a once widespread formation which probably extended over the whole of North Gippsland. The sketch section which I have given (fig. 8) will, to a certain extent, show the facts ob- servablo at Bindi, Tabberabbera, and other places, from which it is evident that the denudation to which that formation was exposed re-