OCEANOGRAPHY 1961 — PHASE 3 187 



concerned with mineral and petroleum exploration geophysics, as 

 opposed to the broader interests of the American Geophysical Union. 



A great many members of the SEG belong to the AGU as well; 

 also to the Seismological Society as well. There are a number of 

 societies. But this one in particular is concerned with the interests 

 of the minerals exploration industry. By "minerals," I am including 

 oil as well as solid ores. 



Mr. Miller. Before this was reduced to a science for the applica- 

 tion of applied research in the field, seismic work, by exploding a 

 charge, measured the density of the earth? 



Dr. Blake. It is an echo sounding thing. 



Mr. Miller. Prior to that, did you try to locate water with a di- 

 vining rod? How did the people originally determine how to drive 

 wells ? 



Dr. Blake. Largely by surface geology, and there is still a lot of 

 surface geology done, of course. 



Mr. Miller. But you put down a lot of dry wells in surface 

 geology? 



Dr. Blake. The primary function of an exploration geophysicist is 

 to predict structure and rock type and so on at depth on the basis of 

 physical measurements which he can make on the surface of the earth. 



Now, the tool that is most widely used, as mentioned, is seismology. 

 However, we also work with measurements in the gravitational field 

 of the earth, the magnetic field of the earth. We work with artificial 

 and natural electric currents in the earth and other physical phenom- 

 ena of this nature, which we hope will give us clues to the "inner 

 space" in which we find what we are seeking. 



The membership of the society comprises geophysicists both among 

 the consumers of geophysical services, you might say, that is to say, 

 the oil companies and mining companies, and also the purveyors of 

 these geophysical services, the geophysical contractors and the geo- 

 physical instrument manufacturers. 



Now, in some instances the user, the purveyor, the manufacturer, 

 are all one and the same company. Some oil companies, for example, 

 do their own data gathering in the field. They build their own instru- 

 ments. Some of them do this only in part. Other oil companies use 

 the data, but they rely on geophysical contractors to gather it for 

 them, and they rely on geophysical instrument makers to provide the 

 instruments that they need. So that the membership then covers the 

 whole spectrum of the geophysical industry from the instrument 

 manufacturer through the instrument user to the data user. 



Now does that give you a picture, then, of what the SEG is and what 

 our business is ? 



Mr. Pellt. I would like to clear up a statement that the chairman 

 made, a very caustic statement, with regard to the willow wand being 

 used for locating water. Are there any instruments by which you now 

 can determine the presence of the water under the earth ? 



Dr. Blake. There are electrical methods in which we can establish 

 roughly relative probabilities. We cannot definitely say, "There is 

 water here," or "There is not water there" — it is all a matter of prob- 

 abilities — and whether it is oil or water or metals or whatever it is, 

 that we are looking for. 



