PHOSPHATE LANDS. 



131 



be more than three-fourths of the total tunnel and shaft work required to 

 mine the bed, 1 foot of lift being considered equivalent to 7.92 feet of haul. 



D. Where the phosphate bed occurs at or near the surface so that the 

 deposits may be readily mined by open-cut or stripping methods, the minimum 

 thickness of a phosphate bed containing 70 per cent or more of trlcalclum 

 phosphate shall be 3 inches. For beds containing less than 70 per cent 

 trlcalclum phosphate the minimum thickness shall increase to 1 foot as the 

 percentage of tricalcium phosphate decreases from 70 to 30 per cent. 



DEPTH IN FEET 



Example; 4-foot phosphate bed 



60 percent tricalcium phospl 



Maximum depth limit "2,250feet 



PiGUEB 7. — Diagram showing deptli to wliieli phosphate deposits are classified under 



article A of the regulations. 



PROORBBS IN OIiASSIFICATION. 



Classifications of the phosphate lands that have been examined 

 are made according to articles A and D of the regulations. Eecent 

 field work in the closely folded phosphate region in the Western 

 States and in the comparatively shallow deposits of Florida has 

 shown that the attitude of the beds in these localities is such that it 

 is not necessary to make use of articles B and C in 'classifying the 

 lands. The classifications that are made according to the regula- 



