VIEW OF SLIOCH (3,217 feet), LOCH MAREE, ROSS-SHIRE. From a sketch by Sir Arch. Geikie. The central mountain consists of nearly flat Torridon sandstone. The hummocky ground emerging from underneath the sandstone on both sides and in front consists of gneiss and forms part of a group of mountains that existed before the deposition of the sandstone, and is

now being laid bare once more by denudation. The gneiss on the right hand reaches a height of 2,500 feet.

age. Not only do the hills differ from each other in the relative antiquity of their materials, but they also differ in the dates of their definite evolution as prominences on the earth's surface. That this statement must be true will be apparent if we reflect that in the crust of the earth there are many successive formations, and that those which lie undisturbed at the top must be younger than those which remain below. But it does not follow that a mountain carved out of the newer formation is necessarily younger than one carved out of the older. We have to consider at what period the process of carving began. It may quite well happen that a mountain group has been cut out of a late series of rocks before, in the course of geological revolutions, an older series was pushed upwards and laid bare by denudation, to be in turn sculptured into mountains.

In no respect are the Scottish mountains more interesting than in the wide differences of age which they manifest. They include a small group of the very oldest mountains in Europe, and also a good many which are among the youngest. The most ancient of all lie out of the way alike of tourists and mountaineers. I am not aware that any members of our Club have ever set foot on them. They rise to the east of Loch Maree, and extend towards the hollow of Little Loch Broom. (Plate D.) There is nothing peculiar in their forms to distinguish them from their much younger neighbours. It is not until we begin to study their structure that we realise that in these scattered hills we have before us a fragment of primeval Europe. They take us back to an age anterior to the appearance of the oldest known forms of life upon the surface of the globe-to the very beginning, as it were, of geological time. They have been preserved all through the long cycles of the past by having been buried under the sediments of the sea or lake in which the red sandstones of Applecross and Torridon were deposited. As they sank into these waters, their slopes were, step by step, submerged under sheets of gravel and sand, until their highest summits disappeared. How deep a mass of rock once covered them it is impossible to tell. But it was enough to protect them until a comparatively recent time. One by one they are emerging again to day

light, as their mantle of hardened shingle and sand is being stripped away from them. You can climb their sides, one foot on the red conglomerate that marks their former shorelines, and the other on the grey gneiss that rose above the water into dry land. One of these re-excavated mountains, A'Mhaighdean, a little to the north-east of Ben Slioch, rises to a height of three thousand feet above the sea. They must have formed a varied group, with winding valleys between them, carved out of the oldest rock in Europethe fundamental gneiss.

The rest of the Highland mountains are modern in comparison with these monuments of antiquity. Yet they, too, differ a good deal in relative age. Their materials have undergone gigantic crushing and dislocation. Enormous masses of the earth's crust, many miles in length and thousands of feet thick, have been driven over each other, and it has been out of this compressed, plicated, and fractured material that the main mass of the Highlands has been carved. The geologist who wanders over the wilds of our mountains, while he meets at every step with tokens of the stupendous forces that came into play in the piling up of the rocks, is everywhere likewise reminded that the present forms of the hills are not aboriginal, but have resulted from the action of the denuding forces, prolonged through inconceivably vast periods of time.

In fine, as one more illustration of the element of relative antiquity in our mountain system, I may allude to the piles of material heaped up by our latest volcanoes. In a geological sense these eruptions ceased, as it were, only yesterday. They go back no further than older Tertiary time-that is, they are younger than the clays, sands, and gravels of the London basin. When they took place, Scotland probably stood at least five or six hundred feet higher than it does now. All along the west of the country, in the long depression, then probably a terrestrial plain, between what are now the mainland and the chain of the Outer Hebrides, there stretched a wide sea of lava, poured forth from many scattered vents until it had accumulated to a depth of more than three thousand feet. Here and there, below this volcanic plain, the subterranean forces protruded huge