PHOSPHATE LANDS. 125 



PHOSPHATE RESERVES. 



In order to prevent the alienation of the phosphate deposits on 

 the public lands until Congress shall provide a law for their disposi- 

 tion that will encourage development under conditions favorable to 

 the public interests, the known phosphate lands remaining in Gov- 

 ernment ownership have been temporarily withdrawn from entry. 

 The reserves thus created embrace lands in the phosphate belt of 

 Florida and in Utah, Idaho, Wyoming, and Montana. 



IXOBTDA BESEBVSS. 



The deposits in the Florida reserves include two important kinds of 

 phosphate — ^the hard rock and the land pebble ; the latter doubtless 

 was derived fronf the former. Deposits of both these types are found 

 near the surface and are mined after removal of the soil cover or over- 

 burden. The pebble deposits are fairly regular in thickness, but the 

 hard rock occurs in irregular pockets in the limestone of which it is 

 supposed to be a residual product. The pebble deposits cover a large 

 area, mainly in southwest-central Florida; the hard-rock deposits 

 are distributed through the northwestern part of the State. 



The hard-rock phosphate is sold on a guaranty of 77 per cent of 

 tricalcium phosphate (the bone phosphate of commerce) and the 

 pebble phosphate on guaranties of 60 to 75 per cent. 



The prospecting or geologic mapping of these practically flat de- 

 posits in a region of slight relief is in most places complicated by 

 ihe presence of overburden, so that any investigation of undeveloped 

 portions is conducted principally by systematic drilling. 



WSSTEKET BESSBVIESS. 



The phosphate deposits in the western reserves consist of rock 

 phosphate occurring in beds interstratified with other rocks, in 

 much the same way as coal occurs. The beds over i feet thick con- 

 taining 70 per cent of tricalcium phosphate are from one to three in 

 number in different places. These are interbedded with yellowish 

 to brown phosphatic sandstone and shale and here and there with 

 thin beds of dark limestone. The shale contains from 25 to 60 

 per cent of tricalcium phosphate and is doubtless of future economic 

 importance. The phosphatic series ranges from less than 6 feet 

 to about 180 feet in thickness and usually lies between a light- 

 colored sandy limestone of variable thickness and a white, brown, 

 yellow, or dull-black cherty limestone averaging 225 feet in thick- 

 ness. The chert overlies the phosphatic beds where the strata are 

 in normal order, but in places the beds have been turned completely 



