phosphoric acid, but as a rule it contains 1 to 2 per cent of nitrogen, 
10 to 20 per cent total phosphoric acid, and 3 to 10 per cent of citrate- 
soluble phosphoric acid. Small amounts of nitrates and water- 
soluble potash are often present. Samples Nos. 458, 497, 733, and 
734 are representative of this class of guano. 
Phosphatic guano. — Phosphatic guanos represent what may be 
called the end product of the various reactions and conditions which 
produce the decomposed guanos. Practically all organic matter has 
been oxidized, leaching has carried away all the potash, gypsum, and 
nitrates, and the monocalcium and dicalcium phosphates have been 
converted into tricalcium, ferric, or aluminum phosphates. The 
phosphatic guano, though somewhat similar in appearance to the 
decomposed guano, has a greater volume weight and is generally 
more gritty in texture and lighter in color. Sometimes .the color 
is red, owing to the presence of much iron, but it is more generally 
light brown or gray. Phosphatic guano contains practically no 
nitrogen and consists of the insoluble phosphates of lime, iron, or 
alumina, mixed with siliceous impurities. The total phosphoric acid 
content is high unless the amount of siliceous impurities is high. 
Samples Nos. 500, 501, 504, and 509 are of this type. This material 
is physically and chemically similar to old, leached bird guano. 
CONDITIONS AFFECTING THE COMPOSITION OF THE DEPOSITS. 
The great variation in the guano in the same and different caves 
can not be well understood without considering the various condi- 
tions affecting the material. The composition of a guano is deter- 
mined by its age, the amount of water entering the cave, the intrusion 
of soil from without, and the composition of the limestone or rock 
forming the floor of the cave. 
The age of the deposit is of slight importance in determining the 
nature of the material except as it affects the completeness of other 
modifying influences. 
The amount of water entering the cave doubtless affects the 
material more than any other condition. A cave where no water 
enters and where the atmosphere is yet sufficiently humid to promote 
bacterial decomposition is likely to contain a guano high in nitrates, 
potash, phosphoric acid, and soluble salts ! or a product richer than 
the fresh manure, owing to the decomposition of the bulky organic 
matter. Absolutely dry conditions, such as obtain at the Peruvian 
guano deposits, where moisture is insufficient for much bacterial 
decomposition, will most probably produce a guano of practically 
the same composition as the original material. 
Neither of these extremes exist in Porto Rico, as surface or 
percolating water enters all the caves at times. Where material has 
i Sample No. 881 approaches this material. 
