Seismic prospecting or surveying constitutes one of the most important geophysical diagnostic methods; knowledge of the wave velocities in different materials is evidently a primary requirement, to which a great deal of effort has been devoted in the field and laboratory. Unfortunately for the sensitivity of the diagnosis, a given material is not characterized by a unique set of velocities, different from those of all other materials. For each material, the velocities depend upon a number of factors, such as alteration, present and perhaps former depth, and in some cases moisture, direction with respect to schistosity, bedding, and so on. Thus a range of values must exist even for a fairly well defined material, and this range frequently overlaps, to a large extent, the ranges of other materials. A velocity determined in the field for a more or less well-defined formation will represent an average for the varying conditions within this layer along the path of the wave; for different depths of penetration, different conditions and hence different velocities may be expected. The determinations which have been published are not adequate for the formulation of definite relations between velocity and the various other factors except . . .