ORIGIN OF NITRATES IN CAVERN EARTHS 131 
evaporated in a platinum dish and the residue was analyzed. A 
sample of cave earth collected as nearly as possible beneath the 
spot where the sample of subsoil was taken, was also treated in 
the same way. A sample of bat guano and one of the earth 
occurring just below the guano were subjected to the same 
treatment. The results of these several analyses are given in 
the following table, the figures representing percentages of the 
sample taken: 
Mammoth. Cave Dixon’s Cave 
Subsoil over Cave earth Earth below 
Mammoth Cave below at (gLeine bat guano 
Sulphunteacidsts Oomacem ac 0.0054 4.16 0.67 0.031 
Wimess Ca@ ion cgerepeetessicees 0.0018 2.03 3.34 0.23 
Alkalis, Na,O, and K,O... 0.00288 2.86 0.37 0.26 
Phosphoric acid, P,O;..... trace 0.0003 0.044 0.0137 
Jmmnvorneys INalas sogaso se 8e 0.00192 0.011 0.102 0.019 
INGE NCIS INGO Ga gaa boc6 0.0068 0.82 6.016 0.0118 
By comparing these analyses it is evident that the soluble 
material in the cave earths might have been leached from the 
soil above. 
The bat guano forms a thin layer over the floor of Dixon’s 
Cave, and is composed of a mixture of excrement and fuzzy 
material from the bats’ bodies, together with sand and earthy 
matter from the walls of the cavern. Judging from the above 
analyses, this layer seems to have acted as an excellent absorb- 
ent preventing the further percolation downward of material 
dissolved from the soil above the cave, since the earth below con- 
tains very little soluble material. 
But guano was found to contain considerable amounts of 
salts of phosphoric acid soluble in cold water, while the cavern 
earths proper contain only traces of these salts. The total per- 
centage of phosphate dissolved out of bat guano by dilute acid 
was found to be about the same as that derived from cave earth 
by the same treatment. The following results of analyses of bat 
guano, taken just as it came from the cave, making no attempt 
to mechanically separate the sand and earthy matters, and of cave 
