358 



REPORT OF NATIONAL MUSEUM, 1899. 



crystalline aggregates, as in Canada and Norway, that the material 

 has any great economic value. The average composition of the apa- 

 tites, as given in the latest edition of Dana's Mineralogy, is as follows: 



The name phosphorite covers a material of the same composition as 

 apatite, but occurring in massive concretionary and mammilary forms. 

 (Specimens No. 37M7, U.S.N.M., from Spain and 60741, U.S.N. M., 

 from Florida). The name was first used by Kirwan in describing the 

 phosphates of Estremadura, Spain, which occur in veins and pockety 

 masses in Silurian schists, as noted later. 



Rock phosphate. — The general name of rock phosphate is given to 

 deposits having no definite composition but consisting of amorphous 

 mixtures of phosphatic and other mineral matter in indefinite propor- 

 tions. Here would l)e included the amorphous nodular phosphates 

 like those of our Southern Atlantic States (Specimens Nos. 34322, 

 44244, 66737, U.S.N. M.), phosphatic limestones and marls (Specimens 

 Nos. 62718, U.S.N.M., Africa, and 62723 Utah), guano (Speci- 

 men No. 69281, U.S.N.M.), and bone bed deposits (Specimens Nos. 

 66581, 67332, U.S.N.M.). These are so variable in character that no 

 satisfactory description of them as a whole can be given. The name 

 coprolite is given to a nodular phosphate such as occurs among the 

 Carboniferous beds of the Firth of Forth in Scotland, and which is 

 regarded as the fossilized excrement of vertebrate animals. (Specimen 

 No. 62731, U.S.N.M.) Phosphatic limestones and marl, as the names 

 denote, are simply ordinary limestones and marls containing an appre- 

 ciable amount of lime in the form of phosphate. Such are rarely suf- 

 ficiently rich to be of value except in the immediate vicinity, owing to 

 cost of transportation. Guano is the name given to the accumulations 

 of sea-fowl excretions, such as occur in quantities only in rainless 

 regions, as the western coast of South America. The most noted 

 deposits are on small islands off the coast of Peru. The material is of a 

 white-gra}^ and yellowish color, friable, and contains some 20 or more 

 per cent of phosphate of lime, 10 to 12 per cent of organic matter, 30 

 per cent ammonia salts, and 20 per cent of water. Through prolonged 

 exposure to the leaching action of meteoric waters, like deposits in the 

 West India Islands have lost all their ammonia salts and other soluble 

 constituents and become converted into insoluble phosphates, or 

 leached guanos like those of the Navassa Islands. (Specimen No. 73243, 

 U.S.N.M., to be noted later; and also specimens from the Grand Con- 

 netables, French Guiana, Nos. 73069 to 73075, U.S.N.M., and Redonda 

 Nos. 53147 to 53152, U.S.N.M.) 



Origin and occurrence. — The origin of the various forms of phos- 



