_Fourth_, That over all the solid rocks, almost everywhere is spread a covering of this loose, and, for the most part, drifted matter, consisting of sands, gravels, and clays. These overspread not only valleys and plains, but hill-sides and slopes, and sometimes even mountain-tops, to a greater or less depth. There are comparatively few spots where these loose materials do not cover and conceal the native rocks; but in some localities, and especially in wide plains and deep river valleys, they are sometimes met with in accumulations of enormous depth. In our own island, a depth of two hundred feet of such superficial sands, gravels, and clays, is by no means unusual. They are often sorted into beds alternately coarse and fine, evidently by the action of moving water; and while the great bulk of the fragments of which our English gravels consist can generally be traced to native rocks at no great distance from the spots on which they rest, yet among them are to be found fragments also, which must have been brought from Norway, and other places, many hundred miles distant. On the surface of these drifted masses we generally live, and from the soils they form we extract by tillage the means of life. _Fifth_, That these, occasionally thick, beds of drifted matter—_drift_ we shall for brevity call it—are in some places cut through by existing rivers, the beds of which run between high banks of clay, sand, or gravel, which the action of the stream has gradually worn and washed away. This is seen in many of our own river valleys; and it is especially visible along the great rivers of North America. The effect of this wearing action is to remove, mix up, and _re_distribute, towards the river’s mouth, the materials which have been scooped out by the cutting water, and thus to produce, on a small scale, along the river’s bed, what had long before been done in the large, when the entire bed of drift through which the river flows was itself spread over the plain or valley by more mighty waters. These things being understood, a very wide geological examination of gold-bearing localities has shown— _First_, That gold rarely occurs in available quantity in any of the stratified rocks, except in those which belong to the primary or oldest group, and in these only when or where they have been, more or less, disturbed or altered by ancient volcanic or volcanic-_like_ action; by the intrusion, for example into cracks and hollows, of veins and masses of serpentine, granite, syenite, and other igneous rocks, in a melted or semi-fluid state. _Second_, That among these primary stratified rocks a subdivision, to which the name of Silurian was given by Sir Roderick Murchison, has hitherto, as a whole, proved by far the richest in this kind of mineral wealth; though the slate-rocks below, and the sandstones and limestones above, in favourable circumstances, maybe equally gold-bearing.