8 
been exposed to a flow of water through the mouth of the cave or 
through holes in the roof, it contains very little soluble material. 
Where only a small amount of water percolates through the rock, 
the guano may contain considerable soluble phosphates, gypsum, 
some nitrates, and ammonia. In some cases a leached phosphatic 
guano is enriched, possibly only temporarily, by the infiltration of 
soluble phosphates, nitrogen, and gypsum from other parts of the 
deposit. The accumulations of gypsum which sometimes occur in 
certain parts of a deposit are evidently due to the evaporation of 
leaohings from other parts of the deposit. 
Aside from the translocation and removal of soluble materials, 
water affects the composition of a guano by influencing the course 
of bacterial decomposition. In some instances quantities of fresh 
manure have become so saturated with water as to undergo an 
anaerobic bacterial decomposition, probably similar to that resulting 
in the formation of peat. Similar material is formed when a layer 
of fresh manure becomes covered with a crust of carbonate of lime 
or a slide of other guano. This material is not very common, but 
is easily recognized, as it is black rather than brown in color and 
shrinks enormously on drying. It contains a large amount of organic 
matter and considerable nitrogen. Samples Nos. 502 (Table III) 
and 786 and 982 (Table IV) represent this material. 
Occasionally earth is carried in through the mouth of the cave or 
through holes in the roof which, becoming admixed with the guano, 
renders it of little value. Samples Nos. 802, 804, 805, 813, 919, 
1007 (Table IV) are representative. 
The character of the rock forming the cave determines largely the 
composition of the leached or phosphatic guanos. Where the cave 
is formed in pure limestone and there are no intrusions of soil, 
the phosphatic guano consists chiefly of tricalcium phosphate. 
This is true of some of the leached bird guanos found on Mona Island. 
Where the rock, however, contains considerable iron, alumina, and 
silica, or these elements are brought in by water, the phosphatic 
guano may consist largely of phosphates of iron and alumina with 
siliceous impurities, as shown by the analyses of samples Nos. 501, 
504, 505, and 509 (Table III). 
VARIATION OF MATERIAL IN THE CAVE. 
Most caves contain a large number of different kinds of guano, 
varying from the fresh bat manure to the leached phosphatic guano. 
While the general classes of material are more or less apparent to the 
eye, little can be told about the percentages of the fertilizing elements 
from the appearance. 
Hardly any rule can be given concerning the variation in guano in 
different parts of a cave. In some cases the guano below the fresh 
