The First impression one gains, from walking in many parts of the Kosciusko National Park, is that the ground beneath ones feet is mainly soil, although it often contains rock fragments and large boulders. Only along the floors and lower slopes of the deep mountain valleys is it common to find exposed extensive areas of solid rock. Yet, the mountains are essentially composed of these solid rocks with the soil forming only a thin, but vital layer over them.

The underlying rock can also often be seen in the lower parts of deep road cuttings, and it has been extensively explored for the dams, tunnels and power stations of the Snowy Mountains Hydro-Electric Scheme.

The main groups of rocks and a summary of their geological history are given in Table 1 and in the Location Plan.

The greatest part of the bed-rock consists of granite in several varieties. The most common is a grey rock composed of colourless glassy quartz, opaque white feldspar, and black mica.

Some varieties have a distinct foliated, or layered, appearance and therefore are called granite gneiss. An example is the white gneiss forming the summit of Mt Kosciusko. The foliated structure is due to the rock having been subjected to intense stress, either when still plastic during the last stages of its consolidation from the molten state, or while solid.

The granites, in many places, have been decomposed by weathering and have broken down to a yellow-brown sandy soil, which may be many feet in thickness. The partly-weathered still solid granites are usually yellow-brown in colour. Often isolated masses of granite, which have resisted weathering better than their surroundings, form large, rounded boulders or groups of boulders many metres across. These are called “tors.”

There are many other varieties of coarse-grained igneous rocks but they mostly occur only locally. over small areas. Between Kiandra to the north, and Geehi Dam to the south, there occurs a series of elongated masses of dark grey, almost black diorite, gabbro or hornblendite. The most conspicuous of these forms the summit of Jagungal.

Another interesting rock is serpentine which occurs as a narrow but continuous belt for 40 kilometres between Tumut Pond and Buddong Falls south-west of Talbingo. Some varieties of serpentine are yellow-green to dark green in colour, very soft and soapy to the feel, like talc, which often occurs with it.