Alkalis In Colorado 
25 
result. We have these facts: The surface soil is extremely rich in 
nitrates; the ground-water is also very rich, while the water from the 
shales carries none at all. The shales then cannot be the source of the 
nitrates that we find on the surface of the land, nor in the ground- 
waters. Evidently the nitrates in the ground-waters came from the 
surface soil. 
We have the following facts to help us answer the question Where 
do the nitrates come from ? The mass of the mountains does not con¬ 
tain them, they are not brought to the lands by irrigating waters; they 
do not come out of the shales even when these are present. In this 
connection I will call attention to the fact, that, in discussing this point 
in Bulletin No. 155, the first one this station published on the occur¬ 
rence of nitrates in soils in injurious quantities, and I believe the first 
one ever published on this subject, I said: “This, (Referring: to a sug¬ 
gestion that I had previously maide to the effect that these nitrates migh’:, 
in some cases at least, be derived from the shales), can all be answered 
very easily by stating the following facts: The mesas above these shales are 
cultivated and bad nitre spots occur on top of them, in one case 80 feet 
above the level at which the water was taken; second, that nitre spots 
* 
occur in entirely idifferent geological formations where these shales do not 
occur, in alluvial deposits and under ordinary prairie conditions, in other 
words, the shales, considered as a source of the nitre, would not be ade¬ 
quate for the explanation of the greater number of occurrences and, in¬ 
dependent of any other reason, than their insufficiency, we must seek for 
a more general source, or a cause sufficient to account for all of the oc¬ 
currences, assuming that they have a common cause, which is reasonable, 
at least, until we are sure that they have different causes.” 
The nitrogen in these nitrates never forms a component of the 
rocks in the sense that soda or potash or phosphorus does and there 
is no great store of this nitrogen laid up anywhere to be changed into 
these nitrates. The only stored-up nitrogen that we have is in coal, 
a vegetable residue, or in these nitrates themselves, which are final 
products in the oxidation of organic or ammonic nitrogen. On the 
other hand, we find nitrogen and nitrates in all soils. This nitrogen 
is of vegetable or animal origin, we think mostly of vegetable origin, 
and the nitrates are found in the soil mostly at the surface. If we 
find them below the surface, say at 3 or 4 or perhaps 9 feet, they have 
been washed down there, in all probability, by downward moving 
water, for they are easily soluble and the soil particles do not hold the 
nitrates back as they do some other salts. These brown spots contain 
nitrogen and nitrates too in much larger amounts than the soil just 
outside of them. These spots are sometimes only a foot or two across 
