PREVENTION OF EROSION BY TERRACING. 7 
The bench type of terrace is subdivided into two classes, the hori- 
zontal and the sloping, the essential difference between the two being 
shown clearly by figure 1. Practically all terraces of the bench type 
are level, which means that they have no fall along the direction of 
their length to drain off surface water to the edges of the field or to 
an outlet channel. 
The ridge type of terrace is subdivided into two general classes, the 
graded and the level, depending upon whether it has fall in the 
direction of the terrace to carry off the surface water. Graded and 
level-ridge terraces are subdivided further into two classes with re- 
spect to breadth of base, namely, the broad-base and the narrow- 
base forms. The broad-base graded terrace is subdivided again with 
HORIZONTAL BENCH 
BENCH TYPE 
SLOPING BENCH 
weer em eee eM ee eK ee 
TERRACES Narrow Base 
LEVEL 
Broad Base 
RIDGE TYPE 
Narrow Basen) tens ee 
GRADED 
Uniform Grade 
Broad Base 
Variable Grade ‘ 
Fic. 1.—Classification of terraces. 
respect to grade, the uniform-graded and the variable-graded ter- 
races. Figure 2 shows actual profiles taken on terraced fields and 
ilustrates the various types. 
THE BENCH TERRACE. 
Bench terraces, as stated, are of two classes—the horizontal and the 
sloping—depending upon whether the bench is horizontal or sloping. 
There are not many good examples of the true horizontal-bench 
terrace in this country, while the sloping-bench terrace is quite 
common. (See fig. 2-A, and PI. ITI, fig. 2.) This is due to the fact 
that the horizontal bench is developed from the sloping bench by the 
gradual movement of the soil down the slope, owing to erosion, and to 
the use of the hillside plow, which always throws the soil down the 
slope. The time required for the leveling down of a sloping bench 
