283 
LOESS OF CHINA—-BARBOUR 
It is clear from the range of composition shown by these samples 
from widely separated localities, that the reasons for the peculiar 
characteristics common to them all must have a physical, rather than 
a chemical, basis and be a result of the size, shape, and relative posi- 
tion of the grains rather than the minerals that compose them. 
The following two additional analyses have been kindly furnished 
by Dr. W. H. Wong, Director of the Geological Survey, and are 
particularly interesting as supplementing the data given above; 
the surprising similarity of composition of samples from widely 
separated localities is also worth noting. 
Analysis of loess made by the Geological Survey of China 
Loess from | Loess from Loess from | Loess from 
Wei-ning, | ‘T'ai-yuan, Wei-ning, | Tai-yuan, 
Kansu Shansi Kansu Shansi 
- a af —E — —_ = 
Eyes 59. 30 OU25" ll Cae Ose ae cle een se 14. 90 13. 40 
aes as sabes we 11.45 HEY Ml Of OP kee O Se Sea 4. 58 3. 95 
Bee wheal apres dpa te 2.32 BRO: ARO eae oe el Ae 2 1. 80 1.65 
ee eee ee oe ae 1. 55 0 0 a Bia We 2.10 
eee egil Es senertanie . 60 Sina C7 Rb ee Se Sia 20 . 20 
Nett Le en oes e . 20 18 || H2O___-_. . 96 . 64 
MINERALOGICAL AND MECHANICAL ANALYSIS 
Viewed microscopically, loess presents the appearance of Figure 
2 which is a camera lucida drawing of the grains of the Honan loess 
already referred to, enlarged 104 times.°® 
Working at 400 magnifications, it is not possible to make accurate 
quantitative observations on the very finest particles without first 
separating these from the coarser silt grains to which they cling. 
Hence, in the absence of apparatus for elutriation, the material of 
diameters below 0.005 millimeter was disregarded; a major part of 
this is probably clay, with some limonite, but no attempt was made 
to determine physically what percentage of the total amount was 
fine enough to be so graded. Excluding these extremely fine parti- 
cles, the average diameter of 758 grains in this sample was 0.0124 
millimeters. ‘Thus, according to the United States Bureau of Soils 
classification, the bulk of the material falls within the limits of silt 
(0.005-0.05 millimeters). The outstanding features are the angularity 
of the grains (which in many cases are practically free from traces 
of rounding), and the surprisingly fresh condition of the mineral 
grains, many of which are still almost unattacked by weathering. 
The determination of the various minerals proved hard at first, as, 
owing to the extreme fineness of the particles (averaging, as noted 
above, less than five ten-thousandths of an inch in diameter), the 
5 Cf. also G. P. Merrill (7-817), fig. 33, “ Chinese Loess.” 
