4 
Bulletin 99 . 
Our soils on the eastern slope of the Rocky mountains are, for 
the most part, light, sandy loams. The heavier, clayey soils, de¬ 
rived largely from the disintegration of shales, especially of the Ft. 
Benton shales, are apt to come under the class of soils designated as 
gumbo, which, to use the language of an earlier writer, is inimical 
to vegetation. The soils derived from the strata of the Jura- 
Trias may be somewhat clayey, occasionally limey, due to the pres¬ 
ence of calcite or ordinary lime stone, or to the presence of gypsum, 
the latter mineral being of common occurrence in portions of these 
strata. 
ORIGIN OR OUR SOILS. 
The origin of our soils may safely be ascribed to the breaking 
down of the rocks forming the mountains to the west of us. The 
mountains from which the material of the strata of the Jura-Trias 
were derived may not have been the present mountains, but the ma¬ 
terial composing them is so similar to that yielded by the disintegra¬ 
tion of the Front Range, that there is no reason for discussing the 
possible differences in origin. 
The rocks of the mountains are essentially granitic in char¬ 
acter, and the sands and soils derived from their disintegration will 
naturally partake of this character, too. It is a fact that the 
soils from the foothills to the eastern part of the state are sandy or 
gravelly loams, in which the sands and gravel are composed of 
quartz and felspar grains, with some mica plates; in some places 
they may be coarser than in others, especially in river bottoms they 
may be finer, but we have everywhere the same general composi¬ 
tion with but little variation, and this restricted to small sections. 
The base of our soils, mineralogically, is very uniform. The 
fact that they are nearly all sandy loams tells us that these mineral 
grains still possess their mineralogical characteristics ; they have been 
broken and ground to small sizes, but they have not been materially 
changed in their composition. The felspar, hornblende, augite or 
mica are the same rocks that form the mountain masses, only that 
they have been broken up into very small pieces. If we examine 
the red, clayey soils, corresponding to the Jura-Triassic strata, we 
find the same to hold true to a very great extent. The red sand¬ 
stones of this formation show the same facts. 
Such are the salient, mineralogical characteristics of our soils. 
The mineral which can furnish the potash is a felspar, orthocluse, 
which yields slowly to the decomposing action of water and air, and 
to some extent, to the action of the roots of the plants. The total 
amount of potash in our soils is from two and one-quarter to two 
and one-half per cent, of the weight of the soil. A comparatively 
small portion of this, however, exists at any given time in such form 
as to be readily taken up by plants. Before this can take place, the 
