The Soil 
15 
ment that the most of the rock material of this soil came directly 
from the mountain masses in geologically recent times, I am fully 
aware that the disintegration of the red sandstones, and to a less 
extent the conglomerates of the red beds, could give rise to a very 
similar mixture of rock fragments. The following facts show this 
plainly. A sandstone belonging to the upper part of the Upper 
Wyoming, of loose texture and easily disintegrated by soaking and 
judicious rubbing, without any grinding up of its particles, gave me 
the followitg mechanical analysis: 
Sand grains having a diameter greater than two millimeters * 
1.40 per cent.; greater than one millimeter, 26.80 per cent.; less 
than one millimeter, 62.70 per cent.; cementing material, oxid of 
iron, calcic carbonate, etc., 9.10 per cent. The sand grains were 
principally quartz, but there were some grains of feldspar and a few 
flakes of mica. In regard to the fineness of the particles, it will be 
noticed that practically 63 per cent, of the mass of the sandstone 
was as fine as that division of the soil designated “ fine earth,” and 
that this percentage is as great or greater than that of the fine earth 
in two of our soil samples. The alkalies in this sandstone were 
determined and found to amount to 1.30 per cent, of the sandstone;: 
potash constituting 1 per cent., and soda three tenths of 1 per 
cent. The cementing material, mostly calcic carbonate and oxid of 
iron, contained a small amount of these constituents, potash 0.025 
per cent., soda 0.053 per cent., calculated on the sandstone, not on 
the weight of the cementing matter. The alkalies were also deter¬ 
mined in a sandstone from the Lower Wyoming, and found to equal 
2.563 per cent, of the sandstone; potash 0.924 per cent., soda 1.639‘ 
per cent. The potash in each of these cases amounts to about 1 
per cent., and is contained almost wholly in the sand grains, among 
which, especially among the larger ones, feldspar grains are easily 
recognizable. These sandstones do give rise to a soil whose elutria- 
tion would yield a mixture of sand grains somewhat similar to that 
with which we have to do in this study. The characteristics of the 
soil formed by the disintegration of these sandstones are so markedly 
different from those of the one we are considering, that they are not 
even suggested as the possible source of the material, except by the 
most thorough washing of the soil formed from them. 
§ 32. The statements relative to the mineralogical character' 
of the different classes of soil particles are applicable to all of the 
soils which I have analyzed or examined with care, whether close 
to the mountains or as far east as the State line, excepting the soils 
of the valley lying between the hogback formed by the Dakota 
sandstone and the mountains proper. This area, corresponding to 
the outcrop of the red beds, is not wholly covered by this granitic 
soil. There are doubtlessly some sections where the surface soil is 
derived from younger formations, the particles of which have not 
