PH08PHATB LANDS. 139 



ftoation of any tract is the relation of the bed and its outcrop to that 

 tract. If the rocks are in normal position— that is, if they have not 

 been overturned or greatly disturbed by faulting— all the area under- 

 lain by rocks stratigraphically below the outcropping bed and there- 

 fore not underlain by the phosphate bed — may at once be classified as 

 nonphosphate. In order to determine what lands are underlain by 

 phosphate deposits it is necessary to work out from the recorded dips 

 and strikes the structure of the field and to ascertain in what 

 position and at what depth the phosphate beds lie. Wlien these fac- 

 tors have been duly considered and the position of the phosphatic 

 layer has been determined, it is necessary to know the regularity of 

 the phosphate content of the bed, its variation in thickness, and the 

 uniformity of its chemical composition from point to point in order to 

 determine whether or not the tract contains a sufficient amount of 

 phosphate to justify its classification as phosphate land. 



Frequently in considering these factors it is desirable to make use 

 of data of a confidential character which may have been procured in 

 the course of the field examination. Such data, although used in de- 

 termining the classification of the land, never appear on the map that 

 is filed, but for all confidential sections, drill records, or other data 

 only the location is indicated on the map and the material itself is 

 kept separate from the general description and is not open to public 

 inspection. 



PBXNOXPI.ES CONTKOLIiina THE CIiASSrETCAajIOlI OT PHOSPHATE liAND. 



Lands that have been included within phosphate reserves because 

 preliminary examinations indicated that parts of them at least 

 contain valuable deposits of phosphate whose exact distribution 

 could not at that time be ascertained are further examined as soon as 

 practicable and all lands barren of phosphate are recommended for 

 restoration. In order to determine what lands should be so recom- 

 mended and what lands should be retained in the phosphate reserve 

 pending legislation providing for the disposition of phosphate 

 deposits, it is necessary to determine what is and what is not to be 

 regarded as phosphate land. It is very evident that lands which con- 

 tain phosphate beds only an inch or two in thickness or with a con- 

 tent of tricalcium phosphate that is only 2 or 3 per cent of the entire 

 mass or lands beneath which the phosphate beds lie at depths so great 

 that they can not be commercially mined should be considered non- 

 phosphate land. 



BEOTT1,ATIONS FOK THE CLASSEBTOATION OF PHOSPHATE LANDS. 



In order that the restorations and withdrawals may conform as • 

 nearly as possible to the factors that are involved in determining 

 78894°— Bull. 537—13 ^9 



