42 The Colorado Experiment Station 
at least will deem this question as deserving a definite answer espec¬ 
ially as I have found that the waters issuing from the shales under¬ 
lying the mesas carry significant quantities of nitrates. The shales 
themselves when a sufficient quantity of them, 1,280 grams, were 
extracted with water actually showed the presence of a trace of 
nitric acid. There are two samples of waters and one of shale 
They represent three different localities, two of them within 
three miles of one another while the third is more than 50 miles 
from either of the other two. This might mean that the shale area 
is very large and though it contains but a trace of nitric acid it 
might suffice to furnish all of the nitric acid which has been found, 
especially as this water has been issuing from these shales and fill¬ 
ing up the lower portions of the country for a very long period. 
This can all be answered very easily by stating the following facts. 
The mesas above these shales are cultivated and bad nitre spots oc¬ 
cur 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 differ¬ 
ent geological formations where these shales do not occur, in allu¬ 
vial deposits and under our ordinary prairie conditions, in other 
words the shales considered as a source of the nitre would not be 
adequate for the explanation of the greater number of occurrences 
and independent of any other reason than their insufficiency, we 
must seek for a more general source or a cause sufficient to ac¬ 
count for all of the occurrences assuming that they have a common 
cause, which is reasonable, at least, until we are sure that they have 
different causes. 
The occurrence of nitrates in the waters and apparently in the 
shale is susceptible of an easy explanation, i. e., the nitre spots 
which are only exaggerated instances of a general condition, occur 
in the lands above the shales. The water that falls or is put upon 
these lands washes the nitrates down into the shales. The soil has 
no power to retain these salts and this seepage water is simply wash¬ 
ing the nitrates out of the land. The shale from the brick yard was 
saturated with this water and the same water was used in making 
the brick. A trace should be present in the aqueous extract of the 
shale as we find was the fact. 
The effect of the nitre on vegetation has been alluded to; the 
spots where the soil is rich in nitrates is entirely barren. See 
Plate II. The most serious manifestation with which we have yet 
met was the rather sudden death of a large number of apple trees 
mostly in June 1909. See Plate III. Plate IV is a view of the 
same rows outside of the affected area. The leaves began turning 
brown at the apices, then along the margins until the whole leaf 
was involved. See Plate I. Sometimes it did not affect the whole 
tree, only a few limbs being attacked. Other trees, beside apple trees 
