86 GEOLOGICAL RECONNOISSANCE 
A peculiar fatty or oily principle seems to be extracted with the nitre- 
salts, during the leaching of the earth, which, according to J. 8S. Thompson, 
rises in the form of a greasy scum to the surface, during the progress of 
the evaporation, and is capable of saponification with allcalies. 
The quantity of organic matter was too small, in the amount of earth 
subjected to qualitative examination in the laboratory, to be appreciable ; 
we are, therefore, still left to conjecture, from the accounts given of the 
nature of this substance, what it may prove to be.-If it is capable of form- 
ing a soap with lye, as represented, we should suppose it to be one of the 
oily acids ; but, as these are insoluble in water, they could not be taken up 
by the water used to extract the soluble salts from the earth in their un- 
combined state, as’ this fatty principle seems to have been; nor do we un- 
derstand how it could be so readily washed off the hand by simple water, 
as we understand the substance in question to have been. Glycerine, it is 
true, is a component of many fats, which, when set free, is miscible with 
water ; but this is a basic, organic compound, which does not form true 
soaps ; neither has it the greasy feel which the substance contained in the 
nitre-earth is said to have. It is more probable that it may be some com- 
bination of one of the known oily acids, with ammonia, which is soluble 
“in water, as a kind of ammoniacal soap ; from this, when subsequently de- 
composed by the addition of lye, the ammonia may be set free, while the 
stronger alkali, taking its place, combines with the fatty acid to form a 
soap, which finally rises to the surface, when the liquor becomes sufficiently 
concentrated. This is rendered more probable, since by the addition of 
caustic lye to this earth, ammonia is evolved. 
_ It seems likely that the animal matters, present in this earth, may un- 
dergo a gradual change in their native bed, similar to that which pro- 
duces adipocere, but resulting in the combination of margaric, or some of 
the other oily acids, with ammonia, which is more soluble in water than 
that substance. 
We have several pounds of this earth still on hand, and may be able, 
hereafter, to determine the nature of this organic principle, if it exists in 
sufficient quantity to be separable, so that it can be subjected to the neces-: 
sary tests for its determination ; if not, we must trouble Mr. Thompson to 
collect, the next time he has occasion to make saltpetre, some of this sub- 
stance from his kettles, for future special investigation. 
About a mile below J. 8. Thompson’s, an escarpment of silico-calcareous 
beds runs along the western borders of Cave creek, the lower layers of 
which, decaying faster than the superincumbent mass, have formed a deep 
recess beneath overhanging ledges. One of the early settlers in this part 
