MINERALS OF THE UNITED STATES — PEHRSON 



185 



expanded much over present rates and a decline is anticipated in a 

 decade. The production of petroleum already is reported to have 

 reached or exceeded optimum rates and any increase in output at this 

 time would be at the expense of efficient recovery. For the remaining 

 minerals shown on the chart decreasing rates are likely within a rela- 

 tively few years. 



SUBMARGINAL RESOURCES 



The foregoing analysis indicates that some of our "blue chip" min- 

 eral resources have been depleted to a critical point. This raises a 

 question as to the possibilities of developing our submarginal resources, 

 the order of magnitude of Avhich is shown in figure 6. In this chart 



Figure 6. — Rough quantitative appraisal of submarginal and highly speculative 

 mineral resources in the United States as of 1944. 



an attempt has been made to show the years-supply equivalent of sub- 

 marginal and highly speculative resources. The availability of these 

 resources varies considerably but on the whole is remote because of 

 uncertainties in basic estimates, high costs of recovery, or technologic 

 problems involved in their utilization. Although they represent a 

 substantial potential national asset and offer a fertile field for research 

 most of them must be considered as largely unavailable under any 

 economic conditions that can be anticipated, at least in the next quarter 

 century. 



Comparison of this list with figure 5 reveals that with few notable 

 exceptions submarginal reserves are roughly proportionate to com- 

 mercial reserves. No estimates of submarginal resources of coal are 

 available, but in view of the large known quantities of commercial 

 coal, such estimates would be of academic interest only. Noncom- 



