9 
The Soil. 
was to be expected that growing plants might obtain some potash 
from this source, but my experiments show that this plant may per¬ 
fect its growth, obtaining all of its potash from the pulverized feld¬ 
spar. 
§ 13. This fact is of great importance to our Western agricul¬ 
ture, especially to the agriculture of the eastern slope of the' Rocky 
Mountains and eastward to the State line, as the irrigable lands are 
composed largely of granitic materials and consequently contain a 
more or less considerable quantity of feldspar, whose decomposition 
yields, slowly it may be, but a continuous supply of this very im¬ 
portant compound. The partially altered mineral possibly presents 
a greater degree of resistance to further decomposition than the 
fresh mimeral does to the first attack, but this will affect only the 
rate of the supply, for we know that this mineral eventually suffers 
complete decomposition. These soils, or mixtures of minerals, 
quartz, feldspar and mica, are well preserved because our climatic 
conditions have not been favorable to their decomposition, either di¬ 
rectly or through the decay of organic matter. The rate of change 
under more favorable conditions, those of irrigation with an increase 
of vegetable matter, may be more rapid, but it will still be compara¬ 
tively slow; not too slow, however, to make its results a factor in 
the supply of potash for our cereal crops. 
§ 14. A question arises in this connection relative to the 
course which the decomposition of the feldspar takes, and whether 
an experiment with powdered feldspar is comparable with the con¬ 
ditions which prevail in the soil. There is no question but that 
they are not wholly so. The decomposition may go on either more 
rapidly or less rapidly in the soil than in the experiment with a 
mixture of sand and feldspar in boxes. Still the results are, in a 
measure, comparable. The soil contained from 16 to 28 per cent, 
of dust, the particles of which have a diameter of less than 0.01 
millimeter, and while, as previously intimated, the original feldspar 
present may have already been so changed that its further decom¬ 
position may be somewhat slower than at some previous stage of its 
historv, it has not been removed from all further action of the 
solutions in the soil, the plant roots and other agents. 
In experimenting with the feldspar, the whole of it was reduced 
to powder, whose largest grains were less than one millimeter in 
diameter, and of which rather more than 33 per cent., by weight,, 
consisted of particles of less than one quarter of a millimeter in 
diameter. The teldspar was pulverized to render it more readily 
attacked, and to reduce its particles to a size comparable with the 
size of the finer soil grains. 
FELDSPAR A SOURCE OF HYDROUS SILICATES. 
) 
§ 15. The water in the soil also shows that such changes are 
