The first formed rocks no doubt became at once the prey of denudation and disintegration, and on their surface would be accumulated the products of their own destruction: newer strata would entirely cover up portions of the original land, to be in their turn succeeded by still later deposits. There is reason to believe that in the remotest ages of the Earth’s history, the forces of denudation and igneous activity were more potent than in later times, and thus the oldest rocks could hardly retain their original structure through the long ages of geologic time. The earliest representatives of organic life were doubtless of such a perishable nature that their remains could not be preserved in a fossil state even under the most favourable conditions. Such organisms, whether plants or animals, as possessed any resistant tissues or hard skeletons might be preserved in the oldest rocks, but as these strata became involved in earth-foldings or were penetrated by injections of igneous eruptions, the relics of life would be entirely destroyed. It is, in short, practically hopeless to look for any fragments of the primitive crust except such as have undergone very considerable metamorphism, and equally futile to search for any recognisable remains of primitive life. In many parts of the world vast thicknesses of rock occur below the oldest known fossiliferous strata; these consist largely of laminated crystalline masses composed of quartz, felspar, and other minerals, having in fact the same composition as granite, but differing in the regular arrangement of the constituent parts. To such rocks the terms gneiss and schist have been applied. Rocks of this kind are by no means always of Archaean age, but many of the earliest known rocks consist of gneisses of various kinds, associated with altered lavas, metamorphosed ashes, breccias and other products of volcanic activity; with these there may be limestones, shales, sandstones, and other strata more or less closely resembling sedimentary deposits. Such a succession of gneissic rocks has been described as occupying a wide area in the basin of the St Lawrence river, and to these enormously thick and widespread masses a late Director of the Canadian Geological Survey applied the term Laurentian. These Laurentian rocks, with similar strata in Scandinavia, the north-west Highlands of Scotland, in certain parts of such mountain ranges as the Alps, Pyrenees, Carpathians, Himalayas, Andes, Atlas, &c., have been classed together as members of the oldest geological period, and are usually referred to under the name of Archaean, or less frequently Azoic rocks. In some of the uppermost Archaean rocks there have been recently discovered a few undoubted traces of fossil animals, but with this exception no fossils are known throughout the great mass of Archaean strata. It is true that some authorities regard the beds of graphite and other rocks as a proof of