212 BULLETIN 42, UNITED STATES NATIONAL MUSEUM. 



gium, and Eussia. Kiver phosphates are by far the most important of 

 the native phosphates. 



The South Carolina phosphates vary in composition from 25 to 28 per 

 cent. pho8i)horic acitl, 35 to 42 per cent, lirae, 2.5 to 5 percent, carbonic 

 acid, and 4 to 12 per cent. sand. 



Ten specimens show the varying character of the river phosphates. 



(1) Ashley River, South Carolina. (34328.) 



(2) Middletou's Place, Ashley Eiver, South Carolina. (34327.) 



(3) Stono River, South Carolina. (3432(;.) 



(4) Cohis Place, Cooper River, South Carolina. (3431G.) 



(5) Bull River, South Carolina. (34321.) 

 (fi) Bull River, South Carolina. (34322.) 



(7) Bull River, South Carolina. (34323.) 



(8) Cast of a Venus shell Coosaw River, South Carolina. (34318.) 



(9) Vertebra. Coosaw Eiver, South Carolina. (34317.) 



(10) Two characteristic specimens. New Hanover County, North Carolina. 

 (44245.) 



PHOSPHATIC LIMESTONE. 



Phosphatic limestones are simply limestones containing more or less 

 phosphate of lime. At present they are not utilized to any extent, and 

 are mainly interesting as being the probable source of the richness of 

 some soils. Tbey are not illustrated in the collection. 



GUANOS. 



Guanos consist, essentially, of the excrement of birds. They are 

 found mostly on small islands where birds are plentiful, especially on 

 the islands of the Taciflc and the West India Islands, although limited 

 deposits are found on the large islands and the continents. The orig- 

 inal deposits contain much soluble material, and sometimes this has 

 been washed out by both sea and rain water, giviug a leached guano. 

 The original or nuieached guanos are found principally on the 

 islands off the coasts of Peru and Bolivia, and are frequently known 

 as Peruvian guano. They contain from 1 to 20 per cent, of nitrogen, 

 10 to 50 per cent, phosphate of lime, 1 to G per cent, potash, and 10 to 

 30 per cent, of water, forming a very valuable fertilizer. They are 

 generally used without any chemical treatment, being simply ground. 

 A single specimen is shown here : 



(I) From the top of Little Bird Rock. Gulf of St. Lawrence. July 9, 1887. 

 (66580.) 



Leached guanos are the insoluble portions of the original guano. 

 They consist of sandy phosphate containing nodules, varying from 

 loosely coherent to quite solid masses, and are also quite variable in 

 composition. They are found on islands near the equator in the Pacific 

 Ocean, and on many of the West India Islands, the most noted being 

 the Navassa and Sombrero Islands. 



