42 AGRICULTURE FOR COMMON SCHOOLS 



which drag over the land and cut and turn it a few inches 

 deep. This kind of harrow is especially useful on sod ground, 

 but is not extensively used. It cannot be used successfully on 

 trashy or stony ground. 4. The disk harrow is made up of 

 a number of disks fastened to a shaft which turns with the 

 disks. These disks are about twelve inches or more in 

 diameter, and cut the ground two to three or four inches deep, 

 according to the angle at which they are set by the regulator. 



A DISK HARROW AT WORK 



The disk is useful to cut clods to pieces and to cut up ground 

 that has become compact. It is also useful on sod ground to 

 cut the sod to pieces and make loose soil. It is frequently 

 used in the spring to cut up corn-stubble ground to prepare it 

 for oats. The disk should be followed by the spike-tooth 

 harrow to level down the ridges and crush the smaller clods. 

 Rolling. — Sometimes the land is so full of large, hard clods 

 that the harrow will not put it into shape without a great deal 

 of labor. The roller is then a useful tool to use. This is 

 sometimes a tree cut into sections and fastened into a frame 



