In most Porto Rican caves the guano forms a layer about 3 feet 
deep over the floor of the cave, although some caverns contain 6 
to 10 or more feet of guano, especially where there are pocketlike 
depressions in the floor of the cave. Most of this material is ready 
for use as it exists. In some cases, however, it contains 10 to 30 
or 40 per cent of stony concretions that should be screened out 
before it is transported any distance. The fresh bat manure requires 
no screening. 
KINDS OF MATERIAL AND MANNER OF FORMATION. 
Although there are no sharp distinctions between the different 
kinds of bat guano, they may be roughly divided into three classes — 
bat manure, decomposed guano, and phosphatic guano. It should 
be borne in mind that this is not a rigid classification, as there are 
all conceivable grades of guanos. The classification is probably 
most useful in considering the formation of the guanos, which will 
be taken up under the description of the three classes of material. 
Bat manure. — Bat manure is, of course, the fresh material voided 
by the hat. Its nature depends chiefly on whether excreted by 
frugivorous or insectivorous bats. The solid material in the manure 
of frugivorous bats consists largely of fruit and berry seeds. Sam- 
ples Nos. 376 (Table III) and 828 (Table IV) represent this material. 
Nearly all Porto Rican deposits come from insectivorous bats, 
the solid matter in the manure consisting chiefly of undigested 
parts of insects, as wings, legs, and other chitinous parts. The 
fresh bat manure is easily distinguished from the older guano by 
its peculiar physical nature. It consists of small excremental lumps, 
is dark brown in color, and when dry glistens somewhat, owing to 
the insects' wings. It has a peculiarly low volume weight, only 
about one-fourth to one-fifth that of other kinds of guano when dry. 
Chemically the fresh manure contains a large amount of chitin, 
the chief constituent of insects' skeletons, as well as a great variety 
of other chemical substances voided by the bat, among which are 
urea and potassium phosphate. The composition is fairly constant, 
as shown by the analyses of samples Nos. 472, 503 (Table III), 751, 
780, 854, 876, 879, 880, 881, 885, and 977 (Table IV): 
Table I. — Results of analyses of 11 samples of bat manure. 
Nitrogen. 
Total 
phosphoric 
acid. 
Citrate- 
soluble 
phosphoric 
acid. 
Maximum 
Per cent. 
13.04 
9.21 
10.93 
Per cent. 
9.74 
2.96 
7.29 
Per cent. 
7 22 
Minimum 
2 01 
