Sea beach gold deposits are mainly derived from ancient gravel beds, which are reconcentrated by being broken down by the impact of the waves and sorted by the waves and tides. As these deposits are in most cases the furthest removed from their original source, the contained gold is of the very finest character, and consequently, the most difficult to save by mechanical appliances; these difficulties becoming steadily greater as the size of the particles of gold diminishes.
If the ocean were operating on solid rocks of any of the various kinds which contain gold, there is no reason to do not find deposits of conglomerate with coarse gold, gradually fading out into finer and finer sediments would be carried by the reflux of the waves or undertow. And further, if the coast line which is being destroyed be gradually sinking, it would be possible to have a bed of conglomerates, consisting of the larger waterworn fragments, extending over a large area, both in breadth and length, fading out on its upper surface into the finer and poorer material, and in some such way as this beds of gold bearing conglomerates may have been formed.
The destruction of the shore line would be more rapid and the deposits more extensive than in those cases where the coast is gradually rising, as in this instance the same material would be longer exposed to the abrading action of the waves, the formation of conglomerates would be less, and of fine sediments more extensive, and the gold particles would suffer more abrasion and be reduced in size. in searching for gold bearing beach sands, these are naturally to be looked for under bluffs of gravel and conglomerate. A favorable time is after a strong wind blowing along the coast line, which makes cross waves, advantageous for concentration. The best spots will usually be those marked by lines and patches of black sand, which are almost always concentrated wherever any gold particle is. Besides, the beach sands proper, gold bearing sands have been worked, off shore, by dredging on the coast of New Zealand.