372 REPORT OF NATIONAL MUSEUM, 1899. 



far the largest of its kind known. As described by Penrose, the 

 "Logrosan phosphate has a subcrystalline structure; some specimens 

 are fibrous and radiating and often resemble feathers. [See Specimen 

 No. 44277, U. S. N. M.]. It is soft and chalky to the touch, easily broken, 

 but difficult to grind into a fine powder. An examination under the 

 microscope exhibits conchoidal figures, interrupted with spherical 

 grains, devoid of color and opaque. (Shepard.) 



" The highest-grade material is rosy white or yellowish white in 

 color, soft, concentric, often brilliantly radiated, with a mammillary 

 or conchoidal surface. Red spots from iron and beautiful dendrites 

 of manganese are not infrequent. The poorer qualities are milky^ 

 white, vitreous, hard, and, though free from, limestone, contain con- 

 siderable silica." 



In the Caceres district the phosphorites occur not in veins but 

 rather in pockety masses in veins of quartz and dark-colored lime- 

 stone, which are found cutting both the granite and slate. (Specimens 

 Nos. 37147, 63779, 63780, U.S.N.M.) 



The following analyses from Dr. Penrose's paper show about the 

 average composition of these phosphorites: 



Logrosan, by Professor Daubeny. 



Silica 1. 70 



Protoxide of iron 3. 15 



Fluoride of lime 14. 00 



Phosphate of lime 81. 15 



Cdceres, by Bobierre and Friedel. 



Insoluble siliceous matter 21. 05 



Water expelled at a red heat 3. 00 



Tribasic phosphate of lime 72. 10 



Loss, iron oxides, etc 3. 85 



Portugal. Phosphorites occur in Silurian and Devonian rocks under 

 similar conditions to those of Spain in Estremadura, Alemetjo, and 

 Beira provinces, and which need, therefore, no further notice here. 

 Stanier, 1 however, describes a variety found in pockety and short vein- 

 like masses which are worthy of a passing notice. These occur not 

 in schists and sedimentary rocks but in massive granites. They are 

 found mainly in the superficial portions, where the granite has weath- 

 ered away to a coarse sand, and in short gashlike veins and pockets 

 of slight width and extent. The phosphatic material is described as 

 of a milk-white color, opaque, and showing when broken open a pal- 

 mately radiating structure, like hoarfrost upon a window pane. As 

 a rule the masses when found are enveloped in a thin coating of kaolin- 

 like material supposed to be derived by decomposition from the feld- 



1 Les Phosphorites du Portugal, Annales de la Societe" G^ologique de Belgique, 

 XVII, 1890, p. 223. 



