The characteristic feature of gold beds deposits is that it is a member of series of stratified rocks, and such was laid down or formed after the rocks on which it rests, and before those which lie on it stop. This peculiarity at once distinguishes a bed from a true vein. A large proportion of the rocks met with consist of substances arranged in distinct stratified layers. If any of these layers consists of a useful gold bearing mineral or contains enough to make it valuable, it is said to be a gold deposit in form of bed, seam or stratum, sometimes known as bedded vein or blanket vein.
The above it is called the roof of the gold deposit and the one below is the floor, when it remains horizontal or nearly so, but when highly inclined the terms hanging wall and foot wall applied to true veins are equally applicable to gold beds, but less expressive. Thickness is the distance from the roof to the floor at right angles to the inclination of the floor, being the shortest distance the roof and floor, and this may be very much less than the length of a cross-cut run through the deposit on a horizontal line, the two becoming nearer in length as the bed approaches more and more to the vertical; in the latter case they would be equal.
Dip is the inclination of the floor from a horizontal plane, and may be indicated in degrees of a circle, as for example five degrees. Other equivalent terms are slope, pitch, underlie and inclination. Dip of course is due to the disturbance of the deposit by elevation or depression, causing tilting or bending, but as such disturbance has been almost universal, nearly all gold bedded deposits have more or less dip at the present time. The strike or course of the bed is the direction of a horizontal line drawn along the floor of the deposit, such as the bottom of a tunnel following the mineral without grade. This direction will clearly be at right angles to the dip of the bed, and will consequently vary as the dip varies; so that, if it is desirable to run a tunnel on a gold deposit in a perfectly straight line, it must have a course or direction as nearly possible at right angles to the general dip, but this is not possible all the time.
Even when the bed may be covered on the surface its position, if it exists beyond the point of discovery, should be traceable by the rocks with which it is associated. The thickness of workable gold beds varies within very wide limits according to their richness in circumstances. But whatever the thickness may be at any particular point, it does not follow that this will be maintained over the entire area of the deposit. Sometimes this may be the case over a very extensive area, but there must necessarily to be a boundary to the deposit in all directions, and toward these limits it may dwindle away to a feather edge with the probability of the greater thickness being near the central portions of the original deposit.