PREVENTION OP 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 



TERRACES^ 



(Narrow Base 



[Level- 



RIDGE TYPE- 



(Broad Base 



(Narrow Base 



(Graded. 



(jBnoad Base ] 



\yar/ab/e Grade 



Fig. 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 

 illustrates 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. Ill, 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 



