492 mckelvey. SEDIMENTARY MINERAL DEPOSITS [Ch. 27 



TABLE 2 (Continued) 



II B. Continued 



Magnesia-caustic calcined, and refractory $ 1,000,000 ?? 



Sodium carbonate (trona, gaylussite, etc) 1,000,000 ?? 



Sodium sulphate (mirabilite, thenardite, etc.) 500,000 ?? 



Total value of production of substances formed by evapor- 

 ation of solvents $ 37,800,000 



III. Detrital-chemical sediments 



Cement, portland (includes cement rock, marl, oyster 

 shells, limestone, clay and shale, blast furnace slag 

 gypsum, sand and sandstone, iron, and miscellaneous 

 materials) $ 292,000,000 



Cement, natural and pozzolan 4,160,000 



Rottenstone 16,000 



Woolrock (included in values for stone) 



Total value of production from detrital-chemical sediments $ 296,000,000 

 GRAND TOTAL (value of production from all types of sedi- 

 mentary deposits) $2,690,000,000 



with deposits of any other origin, and they are associated with the 

 following steps in the production of the mineral or rock: (1) finding the 

 deposit; (2) appraising it; (3) extracting the rock or mineral from 

 the ground; and (4) treating it prior to or during the manufacture 

 of the finished product. These steps are not always clearly defined or 

 inseparable, and not all are involved in the production of minerals 

 from many deposits. 



THE SEARCH FOR SEDIMENTARY DEPOSITS 



The realization that mineral deposits are small in volume and that 

 exploration and mining are expensive has a sobering effect on geologists 

 who, until faced with the actual problem of finding a deposit, think 

 they understand something of the origin and distribution of mineral 

 deposits. Depending on the location, quality, and minability, deposits 

 of manganese, potash, phosphate, and gravel need comprise only about 

 10,000, 40,000, 125,000, and 500,000 cubic feet, respectively, to be of 

 value to small producers. Geologically speaking, even "large" deposits 

 are apt to be very small. Even the most modest exploration programs 

 commonly cost several thousand dollars, and many larger programs 

 cost several hundred thousand dollars or more. The combination of 

 the small size of the deposit sought and the high cost of exploration 



