Page:Quarterly Journal of the Geological Society of London, vol. 35.djvu/53

Rh GEOLOGY OF NORTH GIPP8LAND, VICTORIA. 27

The section as seen at Iguana Creek, commencing at the river- level, consists of alternating shales, sandstones, quartz-grits, and conglomerates. The shales are either without apparent stratifica- tion and of a brick-red or purple colour, or thinly laminated and bluish or greenish grey, and it is in these latter that I have found the plant-remains before mentioned.

Plant-impressions are, however, common, but indistinct in charac- ter, though frequently indicating the ribbon-like character of Gor- daites. The conglomerates are of quartz and other hard and sili- ceous rocks, and together with the sandstones and quartz-grits intermingle and exhibit interesting examples of false bedding and changing condition of deposits. The upper parts of the series are mainly quartzose sandstones ; and some of the lower rubbly shales become locally nodular and calcareous.

The thickness of the series visible at Iguana Creek is probably under 800 feet. The continuity of the beds is unbroken to Tabbe- rabbera, as I ascertained last summer by descending the Mitchell River in a canoe, accompanied by two black fellows, and by that means was able to examine the constant succession of grand natural sections which the rocky gorges of that untraversed river-valley present, which would not be accessible, except in isolated places, by any other means.

Having premised that the Iguana-Creek beds continue in an un- broken manner to Tabberabbera, about 20 miles, I must now, in order shortly to point out the interesting features of this Upper De- vonian group, refer to a locality where the natural sections will be found to disclose the underlying older Palaeozoic rocks, which no doubt elsewhere also underly the Iguana-Creek beds at no great depth.

The valley of the Mitchell River shows at Tabberabbera sections, two of which I have condensed in the sketch, fig. 8. The lower nearly vertical shales, sandstones, and limestones contain Middle Devo- nian marine fossils, and have evidently, together with the still older Palaeozoic sedimentary rocks, been tilted, compressed, and denuded, so that at present their extension to the north is undetermined be- yond a distance of 2 miles from Tabberabbera, and is quite undeter- mined to the east and west. To the south they extend down the Mitchell lliver to near Cobbannah Creek. Lying nearly horizontally on these, the slight dip being southward, we find about from 800 to 1000 feet of sandy shales, conglomerates, and sandstones, principally of a reddish or yellowish colour. We have here the north-eastern escarped edge of the Iguana-Creek beds, Resting on the lowest bed, a red sandy shale, is a sheet of porphyritic and nodular felstone, in which irregular cavities have been filled by agate or quartz, either completely or as geodes. Above this is the remainder of the series of conglomerates and sandstones.

The same sequence of beds is seen in following down the Mitchell River to Cobbannah Creek, where the felstones sink out of sight, and where the overlying sedimentary strata are about 500 feet in thickness. The felstones show as a rugged cliff where last visible,