Page:Quarterly Journal of the Geological Society of London, vol. 35.djvu/39

Rh GEOLOGY OF NORTH GIPPSLAND, VICTORIA. 13

gatta, the "Wongungarra, and the Crooked rivers and their subsidiary- streams. On the western side of the Dargo-River valley, on the line of section, the Silurian strata are exhibited as greenish and bluish clay-slates, alternating with quartzose or micaceous sand- stones, and having a strike to the north-west and a dip of from 70° to 80° to the north-east. On crossing the Dargo River at Mayford, the hillside shows bluish clay-slates of the same direction of strike and dip, but having a somewhat crumpled silky appearance. On ascending the steep eastern side of the valley a gradual change is met with from these last-named rocks, through finely micaceous schists to gneiss.

Although these schists are in places much crumpled and contorted, it is still possible to see that the foliations of the various beds, and the beds themselves, conform to the direction of the strike and dip of the Silurian clay-slates ; and it is important to bear in mind that the dip of the clay-slates, and of the mica-schists into which they seem to pass, is to the north-east, and therefore underneath the more highly altered schists at the summit of the hill. The slope of the ascent is great, and in so far is favourable to observation as re- sembling a cliff-section. The vertical height from the clay-slates of the river to the gneiss at the summit is 1350 feet, and the horizontal distance about from 80 to 100 chains.

This summit is the Great Dividing Range, and from this point there is gently undulating country to within about two miles of the Omeo township. Throughout this distance the following rocks alternate : — Gneiss and gneissoid mica-schist, schistose granite, granites of binary, ternary, and quaternary composition, consisting of orthoclase and quartz, orthoclase, quartz, and mica (principally black), or the three together with black and greenish-black horn- blende.

It is to be remarked that so soon as the schists, in ascending from the Dargo River, become more siliceous, irregular patches or veins of slightly translucent and somewhat greasy-looking quartz appear, forming part and parcel of the foliations. More rarely, veins are met with of coarsely aggregated orthoclase, quartz, silvery mica, and often black schorl, and these are usually associated with the granite schists or the granites (metamorphic).

Other veins are also to be met with of orthoclase, quartz, and fibrolite, all confusedly aggregated together. The fibrolite in places shows certain resemblances in colour and in imperfect prismatic forms to andalusite and even to kyanite. It is found of pale tints of lilac, blue, pink, as well as white, and is exceedingly tough in texture.

The granites are usually met with in the low grounds, in the valleys, but also as small plains at higher elevations. In fact, granites belonging to this division are met with in this locality at all heights, but more generally, as I have said, where streams have cut deep into the schist surface.

In the schists and granites, speaking generally of the whole series, we meet with numerous intrusive dykes, from a few inches