130 WILLIAM HT. HESS 
readily soluble in water by the water which slowly carried away 
the limestone itself during the formation of the cavern. 
Recent progress in bacteriology and agricultural chemistry 
has thrown much light upon the origin of nitrates in soils by 
the oxidation of organic matter in the presence of certain bacteria. 
The surface soil in cavernous regions is usually loose and porous, 
and consequently favorable both for nitrification of organic nitro- 
gen and for downward percolation of the surface water. It may 
not be unnatural, then, to ask whether the nitrates in cavern earths 
may not have orginated wholly or in part from nitrification of 
organic matter at the surface and the subsequent leaching of the 
nitrates so formed into the caverns. Caves would thereby act 
merely as receptacles for the surface drainage, and provide an 
avenue for the return of the percolating water to the atmos- 
phere by evaporation. If the nitrates in caves originated in this 
way, we would expect to find also in cavern earths such other 
soluble constituents of soils as must necessarily have been 
leached out along with the nitrates. 
By leaching cavern earths with cold water some material is 
always extracted. The amount thus washed out is sometimes 
-as much as 13 per cent.of the sample. The following analyses 
are given of the soluble matter of cavern earths derived by ~ 
washing the samples with cold water, the figures representing 
percentages s 
oxide anhydride 
Source Calcium Sulphuric Alkalis | Chlorine Nitric acid | Ammonia 
| 
| 
Mammoth Cave, Ky. 1.06 2a 1.45 0.28 Oo 37 0.005 
Mammoth Cave, Ky. 2520 4.57 3.04 ie dll 1.36 0.001 
Saltpeter Cave, Ind. Ds Bit 32.30 2.26 0.23 1.88 0.007 
From these results it is seem that nitrates form only a small 
portion of the total soluble material in cavern earths. 
A kilo of subsoil over Mammoth Cave was placed in a per- 
colator, and two liters of water charged with carbon-dioxide 
were added and allowed to stand for a week, with frequent stir- 
rings, when the water was slowly drawn off. The water was then 
