APPENDIX. 
THE GUANO-CONTAINING CAVES OF PORTO RICO. 
On account of the many extravagant and misleading statements 
regarding the extent and richness of the guano and phosphate 
deposits in Porto Rico, the Agricultural Experiment Station 
undertook a survey of the guano-containing caves of the island. 
The work was done by Mr. J. H. M. Fallon, who began the survey 
in 1915 and with some interruptions continued it for more than 
a year, 110 caves being explored and the amount and character of 
the deposits being determined. The examination of the caves showed 
that many of them contain more or less valuable deposits of guano, 
which should be more largely used in Porto Rican agriculture. 
The caves have been classified by Mr. Fallon as follows: Caves or 
cavities formed by the fracture and dislocation of strata in mountain 
sides, the caves being entered through horizontal apertures; sink 
holes or vertical cavities, usually circular in outline and of varying 
diameter and depth; and subterranean river beds or passageways 
abraded by the action of sand, gravel, or rocks carried by water. The 
contents of the caves are of two kinds, bat guano and leached bird 
guano. In certain regions the black or blackish guanos are known as 
''murcielaguina," or bat droppings, and all others are called "abono 
mineral," or mineral fertilizer. A more accurate classification 
adopted by Mr. Fallon is: (1) Dry, unmodified bat guano, or new 
guano, (2) modified bat guano, which has lost some of its soluble 
contents through leaching, and (3) leached bird guano, or old guano, 
which is still further described as clean or more or less mixed with 
sand, etc. 
Samples were taken from all the caves for analysis and weighed 
in a box of known capacity, and from the weight per cubic foot the 
amount of the different kinds of guano was estimated in tons. 
Analytical data on the various samples of guano are given in the main 
portion of this bulletin. While many of the caves were found to 
contain little, if any, guano, the tonnage in others was large. In 
most instances the marketing of the guanos will be expensive on 
account of the primitive methods of extracting them and the distance 
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