80 



Penrose, Jr. (1888), all phosphates are divided into two general classes, with 

 the following subdivisions : 



1. Mineral phosphates, embrsicmg \ pP u ' v 



f Amorphous nodular phosphates, 

 I Phosphatic limestone beds, 



2. Bock phosphates, embracing -{ p, f Soluble guanos, 



1 vjuanos St 11 



I ( Leached guanos, 



I^Bone beds. 



" The former includes all deposits of phosphate of lime which, besides having other 

 properties inherent in a true mineral, have a definite chemical composition or at least 

 show a strong tendency toward such properties and composition. The latter includes 

 the deposits which, having no definite chemical composition and lacking the homo- 

 geneous nature and other fixed characteristics of a true mineral, cannot be classed 

 with mineral phosphates." 



Such classification is necessarily somewhat arbitrary; but under its plan 

 the Navassa phosphate would be placed in the second class, and under the 

 subdivision of" leached guano " — i. e., a deposit composed largely or entirely 

 of animal excrement, the soluble constituents of which have been leached by 

 the action of rain and sea water, and the remainder converted into a mass 

 insoluble in water and varying in consistency from a loose powder to a hard, 

 compact rock. 



Many of the AVest Indies, according to the same authority, contain deposits 

 of leached guano, among other islands mentioned being Sombrero, Turk, 

 Aruba, Cura9aa, Orchilla, Arenas, Roncador, Swan, the Pedro and Morant 

 keys, and some of the coral islands and reefs of Maracaibo gulf. 



The character of the phosphate on these several islands varies greatly, and 

 were it not for the large percentage of sesquioxide of iron and alumina that 

 is frequently found these phosphates of the West Indies would be much more 

 desirable than they are for the manufacture of fertilizers. 



Method of Occurrence. — The method of occurrence of both varieties of 

 Navassa phosphate is precisely similar. The material occurs in cavities and 

 fissures in the surface of hard, gray, white and blue limestone, and while 

 there is generally no connection between the irregular, cylindrical pockets 

 and narrow, crooked fissures, they show throughout the island a tendency to 

 rough parallelism, trending about north 20° west and south 20° east. The 

 cavities are rarely over four or five yards wide on the surface, and are often 

 found only sufficiently large to admit a man's body. Occasionally several 

 individual pockets, divided by barren limestone at the surface, may come 

 together ten or fifteen feet beneath the ground and create one large, circular 

 opening. The holes and trenches, indeed, show every conceivable variation 

 of form and outline, and though ordinarily very rough, holes shaped like 

 inverted, truncated cones were seen sometimes with their sides smooth and 

 even as if ^worn and ground by eddying waters. 



