130 DEPARTMENT OF AGRICULTURE GEORGIA. [416] 



that are in the way of cultivation, may be thus utilized, 

 while they are being removed from the cultivated field. 



There are several methods of utilizing rock for drainage 

 purposes, among which are shoulder drains, in which a 

 shoulder is left on each side of the bottom of the ditch, 

 two or three inches wide, with a trench in the center three 

 or four inches wide at the top, according to the volume of 

 water to be discharged, and tapering to two inches in width 

 at the bottom. This center excavation need not be more 

 than four inches deeper than the shoulders. 



Rocks are laid across the centre opening, so as to rest on 

 the shoulders on each side, and straw, sod, or pounded rock, 

 placed above, to exclude fine earth from the centre ditch. 

 This kind of drain can only be used where the bottom of 

 the ditch rests upon very firm clay. 



Shed drains, in which one edge of the rock rests on one 

 side of the bottom of the drain, and the other against the 

 opposite side. 



Fig. 20 Shoulder Drain. Fig. 21 Shed Drain. 



These too will only answer in very firm clay. 

 Box Drains, in which rocks are set against the sides of the 

 ditch, and others placed across them to form the roof of 

 the drain. 



For this drain the bottom of the ditch must be wider 

 than is necessary for either the shoulder or shed drain, 

 since it is not generally practicable to secure uniform flat 

 rock. 



