C. H. HITCHCOCK — THE REDOXDA THOSPHATE. 



of a continuous line of volcanic islands, beginning with Saba, at the northern end 

 and continuing through St. Eustatius, St. Christopher (or St. Kitts), Nevis, Redonda, 

 Montserrat, Guadeloupe and Dominica, and probably farther. Volcanic activity 

 is still displayed in St. Christopher, Montserrat and Guadeloupe. 



Redonda is about one mile long and one-fourth as wide, and its extreme apex is 

 975 feet above the sea level. Most of it is surrounded b}^ a cliflf, never less than 500 

 feet high and reaching to the very top on the western side. The lower cliifs seem to 

 have been formed by the wearing action of the waves, connected with the falling 

 down of loosened fragments by gravity. The cliff is practically inaccessible except 

 by means of the bucket attached to a wire tramway. Multitudes of sea birds nest 

 upon these rocks ; and because of the guano accumulated from their droppings, tne 

 island was occupied for the gathering of fertilizers. After the removal of the true 

 guano a phosphatic mineral immediately succeeded it in depth. This mineral was 

 named Redondite (shortened to Redonite) by the late Professor C. U. Shepard.* It 

 contained, according to him, phosphoric acid, 43.20% ; peroxide of irun, 14.40% : 

 alumina, 16.60%; water, 24 00%: silica, 1.60%; lime, 0.57%. He perceived the 

 strong contrast between this mineral and all other known guanos and phosphates, 

 and noted its similarity to barrand'ite. 



The following are a few analyses selected from a large number made for the English 

 company owning the island : 



P,0, -- -- - 



42.90% 

 8.25 

 24.75 

 22.00 



38.30% 

 11.50 

 21.00 

 20.00 



41.00% 

 10.50 

 19.50 

 23.00 



40.20% 



5.20 

 24.80 

 24.20 



38.20% 

 16.60 



r,o, _ -- __ .- _ 



ALU. _ , _ . _ 



13.40 



H,0 - 



24.80 









97.90 



90.80 



94.00 



94.40 



93.00 



The rock of the island is a lava much like basalt, occurring in sheets resembling 

 strata, and having a dip outwards from the center upon three sides. Many of the 

 sheets are separated by thin and rough porous masses resembling the Hawaiian " aa." 

 At several localities a friable tufa or ash, with breccias, is found to occupy large 

 fissures in the lava. The thicker beds display well the concretionary or columnar 

 structure. The phosphate, called by the miners " crust phosphate," is found to 

 encircle the concretions or spherical nodules, occupying the spaces between them. 

 Imagine a stone wall made of large and small stones cemented together, and the place 

 of a large stone to be often taken by the cement, and let this structure be demolished 

 and the cement gathered into a pile by itself. Then the stones will correspond to the 

 spherules and the cement to the phosphate, and the mining is precisely like the tear- 

 ing down of a wall. The rock is first shattered by blasting, and the phosphate is 

 picked out by hand and carried to the pile awaiting shipment. Mining commenced 

 at the apex of the island, and the mineral has been gathered from several acres of 

 surface, proceeding northeastwardly. There seem to be at least two sheets carrying^the 

 mineral, which are separated by an ash-vein. For ease of working, only the more 

 superficial masses are saved. Several of the bunches have been forty feet wide and 

 deep ; and when of these dimensions they suggest the bonanzas of the silver veins. 

 It is also probable that the phosphate is accumulated along a northeasterly line very 

 much like a vein of metallic sulphuret, but with an absence of walls. 



* Amer. Jour. Sci., 2ad Ser., Vol. XLVII, 



p. 428; also Vol. L, 1870, p. 96. 



