44 Soils of Nebraska — Hicks. 
and forms the surface of the country, thus exerting a more 
dh-ect influence upon the soil than any other formation. This 
influence depends upon the chemical and physical properties of 
the loess. Ln its chemical composition the loess contains all 
the essential elements required in the growth of plants, in so 
far as that growth depends upon the mineral kingdom. Hence 
when the organic matter of the humus is added to loess (some 
organic matter being already contained in the loess itself) the 
happiest combination for a fertile soil is secured. The physical 
properties oE the loess are of even greater importance than its 
chemical composition. It is permeable to moisture, and there- 
fore insures good drainage to the soils formed and underlaid by 
it. At the same time, water does not run through it so rapidly, 
or pass away so completely, as in sand or gravel. Every cubic 
foot of it retains a large amount of moisture, and, since it has 
a thickness of more than a hundred feet in many places, the 
aggregate amount of moisture retained by it is enormous. As 
the surface dries in the heat and drought of summer this retained 
moisture is brought up to nourish the growing crop. In the 
rainy season a fresh stock of moisture is laid up. This storage 
of moisture is much facilitated by the loosening of the surface 
in the operations of tillage. The loess is capable of assuming 
almost the hardness of stone, a fact which accounts for the ex- 
cellent natural roads in Nebraska. By the trampling of animals, 
the sun's heat, and the beating of storms, the natural surface of 
the prairie became hard and nearly impermeable, causing the 
rain-fall to pass off in sudden floods. The breaking up of this 
hard stratum by cultivation causes the retention of a much larg- 
er percentage of the rain-fall, and indirectly increases the rain- 
fall itself. 
The loess is a deposit of sediment in afresh water lake which 
covered eastern Nebraska during a very late period of geologic- 
al history. I have already spoken of another fresh water lake 
in western and central Nebraska, in which the Tertiary rocks 
were laid down. It is difiicult to distinguish between the late 
Tertiary strata and the loess — a fact not at all comforting ta 
the field geologist, but quite the contrary to the farmer in west- 
ern Nebraska. In many counties formed of Tertiary strata the 
upper member is a fine loamy clay or marl, in every respect simi- 
lar to the loess — so similar, indeed, that some geologists have 
