PEBBLE PHOSPHATE ORE DRESSING 39 



made to conform to the depth of the alluvions. 

 For example, a 35-ft. boom will raise material 

 18 to 20 ft. above the shovel track and make a 

 cut 35 ft. wide. The cars to carry the overburden 

 are standard gauge of 12 cu.yd. capacity. They 

 are usually dumped by hand, although some of the 

 more recent cars have air-dumping arrangements 

 which are controlled from the engine cab. The 

 cars are run out to .the dump and handled in the 

 usual manner, care being taken not to waste the 

 material where it will cover future work. Steam 

 shovel work is done by contract, the price being 

 20 cents per cu.yd. 



Whenever conditions are favorable and space 

 available for the disposal of the material, the 

 overburden is removed by the hydraulic method, 

 and pumped into an abandoned excavation from 

 which the phosphate ore has been removed. The 

 cost of stripping by the hydraulic method is from 

 5 to 8 cents per cu.yd. The overburden in Florida 

 phosphate fields is favorable for this kind of work, 

 being clean, fine sand, with some pebbles, the 

 majority of the foreign substances being sods, 

 stumps and palmetto roots. Occasionally the 

 sand is cemented and grades into a soft, but tough, 

 sandstone which must be blasted before hydraulick- 

 ing. Owing to the overburden containing little 

 clay, it can be stacked in large dumps that do not 

 liquefy and run into the streams. 



In Florida where hydraulic stripping is prac- 

 ticed, hydraulic mining may be also, in which case 



