Penrose.] LEACHED GUANO. 123 
dissolved by the action of rain and sea water. It is found most plenti- 
fully on some of the small islands in the Pacific Ocean, northeast of 
Australia, and on many of the West India Islands. It is also found in 
some places on the coast of Chili, as on the promontory of Mexillones. 
Here it occurs as a light yellow phosphatide powder, containing lumps 
of the same substance and averaging 75 to 81 per cent, of bone phos- 
phate of lime. 
Leached guano is found in the Pacific principally on the islands ly- 
ing between longitude 150° to 180° west and latitude 10° X. to 10° S. 
Most of this area was put by Congress under the protection of the 
United States in 1856. It contains some forty guano islands. They 
are all small and low, and are built up by the formation of coral reefs. 
Often there is a salt-water lagoon in the center of the island. Among 
the richest localities are Baker, Howland, Jarvis, McKean, Maiden, 
Starbuck, and Phoenix Islands. The guano is generally pulverulent 
on the top, and more or less solidified below. Occasionally the soluble 
portions have been washed into the underlying coral, forming a phos- 
phatic limestone. The following is a section on Baker Island : 
(1) Pulverulent leached guano, yellow. 
(2) Denser stratum of same substance as (1). 
(3) Coral rock containing gypsum. 
On Jarvis Island a bed of gypsum has been formed by the evapora- 
tion of a central lagoon. Overlying this is a deposit of leached guano, 
from one inch to one foot thick, covered by a phosphatic crust. Under 
this crust tbe bed Contains both basic and neutral phosphate of lime. 
This fact is thought by Dr. C. U. Shepard, jr., to be due to the decom- 
position of the tribasic phosphate by the gypsum. Occasionally con- 
cretionary nodules, composed of interstratified layers of phosphate of 
lime and gypsum, are found. On Maiden Island there is a boggy de- 
posit, which gives off sulphureted hydrogen from the mutual decompo- 
sition of the guano and the gypsum. 
In the West Indies, leached guano has been found on many of the 
coral islands and reefs, all the way from the Bahamas to the coast of 
Venezuela. Among the priucipal localities are Sombrero, Navassa, 
Turk, St. Martin, Aruba, Curacoa, Orchillas, Arenas, Eoncador, Swan, 
and Cat, or Guanahani Islands, the Pedro and Morant Keys, and the 
reefs of Los Monges and Aves in Maracaibo Gulf. The phosphate from 
the different localities varies very much. That from Maracaibo Gulf oc- 
curs in a compact or granular form of a light brown color. Sometimes 
it is distinctly mammillated, and at other times it has a concentric 
structure. It often has a white phosphatic enamel like that which 
covers the basalt of Ascension Island. The deposit contains many fish 
bones, and is rich in phosphate of lime, which sometimes amounts to 
over 85 per cent, of the rock. The Sombrero Island phosphate occurs 
in two forms; (1) As agranular, porous, and friable mass, in color 
white, pink, green, blue, or yellow ; (2) as a dense, massive, and homo- 
(597) 
