182 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 194 5 



underground exploration conducted in active mining areas, and geo- 

 physical methods guided by intelligent, detailed geologic advice have 

 been very successful in locating petroleum deposits. Further de- 

 velopment of concealed resources by a combination of these methods 

 is anticipated but the days of easy and accidental discovery are about 

 Prospecting by geophysical methods is costly, and as the old 



over. 



mines play out, underground prospecting ceases in the well-established 

 producing districts. Additions to known or inferred reserves of most 

 minerals, therefore, depend on technologic progress and the success 

 of exploration that is carefully planned and scientifically executed. 



EXHAUSTION OF COMMERCIAL RESERVES AS OF 1944 



BB Perctnf of original total rtmcintng ! I Ftrcem extracted 



Magnesium 

 Nitrogen 



It ProwJ r*Mn*i only 



Figube 4. — Chart showing proportion of estimated original commercial reserves 

 (measured, indicated, and inferred) of certain minerals in the United States 

 remaining as of 1944. 



The effects of these programs on our mineral reserves obviously can- 

 not be evaluated with assurance at this time and opinion varies widely 

 as to the probable outcome. New deposits undoubtedly will be found 

 as will extensions to known ore bodies not contemplated in present esti- 

 mates of inferred ore. In general, however, I am inclined to believe 

 that the risks and costs involved are too great to warrant the assump- 

 tion that our present estimates will be increased greatly through future 

 discovery. In any event, it is evident that the outlook does not justify 

 determination of national policies solely on the expectation of large 

 additions to our commercial reserves through the discovery of new 

 deposits. 



RESERVES COMPARED WITH PAST PRODUCTION 



To indicate the approximate degree of exhaustion that has occurred 

 to date the estimates of remaining reserves are compared in figure 4 



