AbstractsPhysics

A knowledge of the thickness of overburden is of utmost importance both in ore exploration and in disclosing underground structure. Owing to the cost of drilling and to the fact that geological features upon the earth's surface are not always sufficient, methods for the determination of depth are often sought from other branches of science even if the information so obtained is only qualitative in nature. Giving results not less definite, but having the advantages of simple arrangements and great economy of both time and cost, geophysical methods are now widely used and they have become a powerful and sometimes even indispensable aid to geological interpretation. [...] When the underground structure is simple and known so that the problem can be completely solved theoretically, the experimental determination of depth is a direct one; otherwise, indirect methods must be used in which a certain structure is assumed and the field results are compared with those obtained from a model experiment made to conform to the assumptions. [...] In the following, a review of only two of the geophysical methods, the magne1iic and the electric, are given, since their experimental arrangements are simpler. In the magnetic method, the results obtained on the earth's surface are influenced by all the magnetic properties of the masses surrounding the instrument, whereas in the electric method, the extent of the effective masses may, to a certain degree, be controlled. [...]