Page:Quarterly Journal of the Geological Society of London, vol. 35.djvu/42

16 16 A. W. HOWITT ON THE PHYSICAL GEOGRAPHY AND

the extreme edge of the Omeo basin, where the country rises to form the watershed of the Limestone River. At this place I have noted what seems to be a gradual passage from coarse granite to gneiss, mica-schist, then to a wrinkled and glistening clay-slate, with a high dip to the eastward.

At the Limestone River the rocks are seen to be dark-blue and yellowish clay-slates with narrow quartz veins, and bedded with them greyish crystalline limestone. This group of strata has a general dip to N. 85° W. at 60° to 70°. The crystalline limestones and marbles occasionally show indistinct traces of corals; but so far none have been identified.

(c) Granites. — The granites of North Gippsland may be separated into two classes : —

(a) Those which are the result of the perfect metamorphism of

sedimentary strata ; and,

(b) Those which appear to have invaded, and partly absorbed and

altered, sedimentary strata.

I can feel no doubt as to the origin of many of the granites which are seen alternating with the mica-schist and gneiss of Omeo. A series of rock-specimens can be collected there showing the finest shades of gradation from a true mica-schist to a true ternary granite, or to a quaternary granite, where the fourth constituent appears to be an amorphous green mineral. It is, however, quite possible that in some instances denudation of the schists may have laid bare granites belonging to the second division ; but on this point data are at present wanting.

The second class of granites is met with in numerous localities.

In examining generally the whole district where the Lower Palaeo- zoic sedimentary rocks are visible, it will be seen that granites occur in various places, usually in the river-valleys or as basins of low hills surrounded by Silurian or younger strata (as at Bulgur- back, Dargo Flat, Neoyang, the Lower Tambo river, the Snowy River in its upper course, Deddick, the Genoa River, &c), but are also some- times seen as hills or mountains protruding from among the strati- fied rocks, as at Mount Baldhead, the Forlorn Hope, at the sources of the Tambo and Buchan rivers, and many other places. In all these instances and, indeed, wherever I have met with granites in North Gippsland of this class, their present position, either in the valleys of rivers or as mountain masses, appears certainly to be due to denudation and erosion, subsequent to their invasion of Lower Palasozoic formations.

Some of the broad features to be noted in respect to this class of granite I have already referred to. I may add further that the highly tilted Silurian strata are seen to dip down onto the granite, and to be there cut off either across the direction of dip or of strike ; but in following the general direction of strike of the Silurian strata across the granite, we find that the former recur with the same general direction of strike and dip as before.

The passage from the sedimentary rocks to the granite varies both