130 CLASSIFICATION OF THE PUBLIC LANDS. 



whether a given bed of phosphate possesses any actual or prospective 

 value as a source of commercial phosphate, the following regulations 

 were framed and have been applied in the classification of phpsphate 

 lands. 



The principles incorporated in these regulations are to be used 

 primarily for guidance in determining what lands will be recom- 

 mended for reservation and what lands will be restored or excluded 

 from future reserves. These principles, however, are based on a 

 careful consideration of the factors which affect' phosphate values 

 and which may be involved when provision has been made for the 

 disposition of the phosphate lands or of the deposits themselves. 

 Furthermore, due regard has been given to such future developments 

 as can be anticipated from present conditions. 



Phosphate deposits shall be classified according to their thickness, their depth 

 below the surface, and their calculated tricalcium phosphate determined from 

 phosphoric acid content. 



Lands underlain by beds of phosphate less than 1 foot in thickness or con- 

 taining less than 30 per cent tricalcium phosphate or lying at a depth greater 

 than 5,000 feet below the surface shall be considered nonphosphate lands, except 

 as hereinafter provided. 



A. Lands underlain by beds of phosphate 6 feet or more in thickness and 

 containing 70 per cent or more of calculated tricalcium phosphate shall be 

 considered phosphate lands if the beds do not lie more than 5,000 feet below 

 the surface. The depth limit for beds containing 70 per cent of calculated 

 tricalcium phosphate shall vary from to 5,000 feet in direct ratio to the 

 variation of thickness of bed from 1 foot to 6 feet. For beds containing less 

 than 70 per cent tricalcium phosphate the depth limit shall vary from zero 

 to the depth of a 70 per cent bed of any given thickness in direct ratio to the 

 variation in tricalcium phosphate content from 30 to 70 per cent. 



B. Lands underlain at depths greater than the depth limit given in "A" 

 by horizontal beds of phosphate 6 feet or more in thickness and containing 

 70 per cent or more of calculated tricalcium phosphate shall be considered 

 phosphate lands to a distance of 10 miles from the outcrop or point of accessi- 

 bility from which they can be reached by a horizontal tunnel, which distance 

 shall be decreased to in direct ratio as the thickness decreases to 1 foot. 

 For beds containing less than 70 per cent calculated tricalcium phosphate 

 the maximum distance for any given thickness of phosphate bed shall be 

 decreased to zero in direct ratio as the percentage of tricalcium phosphate 

 decreases from 70 to 30 per cent. If the phosphate beds djp toward the 

 outcrop or lie above the point of accessibility, they shall be included under 

 this paragraph. 



C. The maximum horizontal distance for any given thickness of phosphate 

 bed shall be decreased from that given in " B " to one-fourth that distance in 

 direct ratio as the depth below the outcrop or point of accessibility increases 

 from zero to the limiting value given in "A." This limiting horizontal dis- 

 tance applies both to horizontal and to dipping beds, but in no case shall 

 land be classified as phosphate land where the bed lies at a depth below the 



• point of accessibility greater than that given in "A" or where the amount 

 of barren tunnel and shaft work required to reach the phosphate bed would 



