12 BULLETIN 180, U. S. DEPARTMENT OF AGRICULTURE. 
ment known as an A, which does not require any special skill in oper- 
ating. 1 
KINDS OF TERRACES. 
There are several kinds of terraces in use, such as the guide row, 
the level bench, and the Mangum terrace. The guide-row. terrace is 
formed by throwing four furrows together along the contour line of 
a hill, the furrows following the line of the guide row. A row may 
be planted on top of the terrace to avoid the waste of any land. There 
is generally a drop of 3 feet between terrace rows. This type of 
terracing is used on rather open soil which will readily absorb the 
rainfall, and where the slope does not exceed 10 per cent. 
The level-bench terrace is constructed on steeper lands and is so 
cultivated that the soil is moved from the higher to lower portions. 
In this way the terrace becomes practically level in a few years. By 
plowing with a hillside plow the furrows may all be thrown down hill. 
Quite often this type is developed from the guide-row terrace. Each 
bench must be cultivated separately and farm machinery or wagons 
must not be driven across the terraces, as this will result in their 
quick destruction by forming trenches which develop into gullies. 
Care should be exercised to prevent the growth of weeds along the 
terrace lines, though the presence of grass is often necessary to hold 
the soil. The cultivation may be done in furrows following the con- 
tour, or furrows may be run straight. This latter method results in 
some short rows, to which many farmers object. Probably the best 
method to prevent erosion is to follow the contour. 
The Mangum terrace is one that has attracted considerable atten- 
tion lately because of the fact that it eliminates the uncultivated Hues 
between the terraces and cultivating or harvesting machinery may 
be driven across from one terrace to another. This terrace was first 
constructed and developed by Mr. P. H. Mangum, of Wake County, 
i Any frame in the shape of an A will do. The legs must have the same length and the crosspiece must 
be at equal distances from the ends of the legs. A plumb bob with string attached to the top of the A com- 
pletes the apparatus. 
The center of the crosspiece should be determined, as the A will be in a level position when the line of the 
plumb bob passes through the center of the crossbar. 
In laying off a terrace, one leg of the A is held on a point and the other revolved about it until the plumb 
line crosses the point marking the center of the crossbar. This process is continued from point to point. 
By constructing the A with certain dimensions, it may be used also for determining the grade or slope of 
a field or roadway. The sides are 16 feet long and the crossbar 13 feet 9 inches. A brace 16 feet long may 
be attached by a leather hinge. The ends of the A will then be 16 feet 8 inches apart when set up. 
To use in determining grade, find the center of the crossbar and mark it zero. Then drive two pegs in 
the ground 16 feet 8 inches apart and on a level and set the A on them. The plumb line crosses at zero. 
Raise one end 2 inches and mark where the plumb line crosses the arm 1 per cent. Raise the same end 
2 inches more and mark 2 per cent on the arm, and continue until the one leg has been raised several feet. 
Then repeat the operation on the other side. After the crossbar has been marked, if the A is placed on any 
slope.the plumb line will indicate the grade. The low side of the bar may be marked 2 inches, 4 inches, etc., 
corresponding to 1 per, cent, 2 per cent, etc. A 3-foot fall between terraces may be obtained by moving 
one leg of the A downhill until the plumb bob reading is 36 inches. To obtain differences in elevation 
between two points, run over the line, keeping records of the plumb-line reading, all values going down- 
hill in one column and uphill in another. Add the two columns and the difference between the sums will 
give the difference in elevation of the two points. 
