684 
fication and is likely to produce a range in 
texture and a degree of compactness of the 
lower part of the soil section not found in 
soils formed in other ways. It is often 
difficult to distinguish between material de- 
posited by pure ice action and that modi- 
fied by glacial water due to the melting of 
the ice. 
(f) Wind has not been so distinctively a 
soil-forming agency as water and _ ice, 
though it has very generally contributed to 
the result.° Like water it effects sorting 
and stratification, but the range in texture 
of material carried is very much more nar- 
row, the type of stratification is different, 
and the material has a wider areal unity in 
chemical and physical properties. The 
most distinctive soil formations whose 
origin has been referred to the action of 
wind are sand dunes and loess. The for- 
mer represents a large amount of material 
which has been rolled along the surface of 
the ground. It is usually a fine sand and 
shows sorting to the extent that very fine 
material is almost wholly removed. While 
the origin of loess has been referred to the 
settling of dust from the atmosphere, the 
American deposits exhibit properties which 
cause the adequacy of this theory to be 
questioned. In northern China, where this 
material was first recognized, its origin was 
attributed by Von Reichtofen to the agency 
of wind. At any rate it is a distinct ma- 
terial and seems more closely associated 
with this mode of formation than any 
other. The possible chemical and physical 
properties of wind-blown material entitle it 
to recognition in the scheme of classifi- 
cation. 
IV. The Group—Source of Material.— 
The kind of rock from which a soil is 
formed is generally recognized to have a 
°Free, EH. E., ‘‘The Movement of Soil Material 
by the Wind,’’ Bul. 68, Bureau of Soils, U. S. 
Dept. of Agriculture, pp. 272, 1911. 
SCIENCE 
[N.S. Vou. XXXV. No. 905 
large influence on its chemical and physical 
properties. The mineral character of the 
rock and the extent of decay deter- 
mines the texture of the soil. The com- 
position of the rock influences both the 
composition and texture of the soil in a 
distinctive way. The same rock may be 
transformed into soil by several agencies 
and again the same agency may act on sev- 
eral kinds of rock. The product is likely 
to be equally diverse in its capacity to 
support plants. A large variety of rocks 
might be recognized as influencing the 
character of soils. The fact that soil has 
usually been derived from quite a variety 
of rocks, makes it necessary to keep the 
divisions here as broad as possible, since 
only such can be recognized with any de- 
eree of accuracy. These are rather large 
groups and in practise special distinctions 
are likely to be made on this basis. The 
primary groups to be recognized may be 
mentioned as acid and basic rocks of igne- 
ous origin, and with these the gneisses, 
schists and similar secondary rocks are 
likely to be included; shale and slate, sand- 
stone and quartzite, limestone and marble. 
Plant remains constitute a separate and 
distinct class of material from which soil 
may be formed and the proportion of these 
which enters into any given formation may 
give distinctive character. 
Often the mingling of material from sey- 
eral kinds of rock may impart peculiar 
character to the soils of a drainage system 
or a lobe of glacial ice. The red alluvial 
soils of the Red River drainage system owe 
their character largely to the red Permian 
formations of Oklahoma and Texas. ‘Che 
elacial soils of west central New York are 
largely dependent for their character upon 
the several shale, limestone and sandstone 
rock formations crossed by the ice in reach- 
ing that position. The line of movement 
of the material with reference to the gen- 
