52 The Phosphates of America. 



plied on the inside with steel spirals, arranged around the side like 

 the grooves in a rifle, and heavy streams of water flow into its two 

 ends. The nodules are dumped by the dredge into the small end 

 of the cone and come out at the large end. They are then removed 

 by a derrick to another lighter and towed to shore. 



The dredging machine is not the only means employed for rais- 

 ing the river phosphate, some companies having adopted a contriv- 

 ance consisting of six large claws, which open when they descend, 

 and close, forming a kind of bucket, when they rise. It is said 

 that some of these machines can dredge in 50 to 60 feet of water, 

 while the ordinary dredging boat cannot raise the phosphate in 

 over 20 feet. 



Both the rock and nodules from these river and land deposits 

 occur in very irregular masses or blocks of extremely hard con- 

 glomerate of variegated colors, weighing from less than half an 

 ounce to more than a ton. The mean specific gravity of the mate- 

 rial is 2.40, and it is bored in all directions by very small holes. 

 These holes are the work of innumerable crustaceae, and are now 

 filled with sands and clays of the overlying strata. Sometimes the 

 rock is quite smooth or even glazed, as if worn by water ; at others 

 it is rough and jagged. 



Interspersed between the nodules and lumps of conglomerate are 

 the fossilized remains of various species of fish and some animals, 

 chiefly belonging to the Eocene, Pliocene or post-Pliocene ages. 



Very careful analyses of a large number of the samples of land 

 rocks taken from the pits and made in our laboratory gave, after 

 being well dried at 212 F., the following average : 



Moisture, water of combination and organic matter lost on 



ignition 8.00 



Phosphate of lime 59.63 



Carbonate of lime 8.68 



Iron and alumina (calculated as oxides) 6.60 



Carbonate of magnesia 0.73 



* Sulphuric acid and fluoride of lime 4.80 



Sand, siliceous matters and undetermined 11.56 



Total 100.00 



While it is shown by these figures that the grae of this phos- 

 phate is not extremely high, it has been proved by experience all 

 over the world to be admirably adapted for the purpose of manu- 

 facturing commercial fertilizers, and it will doubtless long con- 



* The sulphuric acid represents the sulphur combined with iron as pyrites. 



