124 The Transactions of the South African Philosophical Society 
on both sides by perpendicular or overhanging cliffs, one hundred or 
more feet high. ‘These cliffs are often so continuous on all sides that 
farmers are able to convert such valleys into camps for their horses or 
cattle, by putting fences across the entrances. 
It is along the base and in the caves of these overhanging cliffs that 
the nitrates and the nitrate-bearing materials occur. The nitrates fill 
the fissures of the laminated rock, and incrustate their surface as finely 
crystallized nitrate of potash, while the soil and débris under the 
cliffs contain a variable amount of saltpetre, which often forms lumps 
more or less pure, or cements the débris of the rock into lumps and 
blocks of considerable size. The richest material is always at the base 
of the cliff, but only in those places where the rock is finely laminated, 
and the overhanging parts protect the foot of the cliff against rain. 
Throughout the whole region which I investigated, and in which I 
spent more than three weeks, I found the source of these nitrates to be 
the refuse and the remains of animals, principally the feces of the rock 
rabbits (Hyraa Capensis). In every single case where the nitrates were 
not accompanied by such remains, I was able to trace their origin to 
caves or crevices in the rocks above containing such materials. That 
similar animal remains are the source of nitrates in most other countries 
where they occur has been known for a long time, and it has been 
shown recently that the nitrification of the ammonia evolved by them 
is due to the action of microbes. 
A. Miintz and V. Marcano* have proved that the saltpetre-earth which 
occurs in the vast caves of the Andes in South America (not to be con- 
founded with the nitrate-fields of Tarapaca in Chili) is being formed in 
this way fromh the guano of birds and bats, and that of the caves of 
Venezuela from bones and fossils. Their attempts to isolate this microbe 
in the usual way failed, because, as was found out later on, it did not 
grow on gelatine or similar mediums. 
A year later, however, Winogradsky+ succeeded in isolating a nitri- 
fying bacillus from soil near Zurich, by a very ingenious and tedious 
method, and he named it Nitromonas, on account of its peculiar shape. 
In 1894 Dr. Tolomei,{ professor at the military academy at Florence, 
published the results of his investigations into the cause of the forma- 
tion of nitre on the walls of some buildings at Florence, and proved 
conclusively that it was due to the action of a microbe. 
Thinking it very desirable to ascertain whether the nitrification in 
the cliffs and caves of the Asbestos Mountains was due to a similar 
cause, I provided myself with sterilized tubes, filled them with samples 
* A. Miintz and V. Marcano, ‘Comptes Rendus,’ 1889, p. 900. 
7 S. Winogradsky, ‘ Annales de l'Institut Pasteur,’ 1890, Nos. IV. and V. 
+ G. Tolomei, ‘Contribuzione allo Studio del Fermento della Nitrificazione, 
published in Le Stazioni sperimentali agrarie italiane, March, 1894, vol. xxvi. , 
