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times parallelogramatic and sometimes crested or trape- 

 zoidal (Fig. 15). The rectangular furrow is the best and 



FIG. 15. TRAPEZOIDAL FURROW-SLICES. 



ploughs that turn up rectangular furrow-slices are the best, 

 other things being equal. (2) The furrow-slices should be 

 laid evenly at an angle of about 45 to the horizontal. (3) 

 The depth to width should be as 7 : 10 (7 inches being the usual 

 depth and 10 inches the usual width of a furrow made by 

 an English plough). The objects of these angles and pro- 

 portions are to expose the greatest surface to the action of 

 air and to allow the harrow passing through the crests to 

 form a proper tilth and seed-bed. When the width is too 

 great for the depth, the furrow-slices lie flat and the harrow 

 has not the same effect. If the depth is too great for the 

 width the furrow-slices stand on edge and show a tendency 

 to fall back. (4) There ought to be a coulter to give the 

 vertical cut that the furrow-slice may turn over clean. (5) 

 The mould-board should so curve backwards that it may not 

 offer too great a resistance to the soil. 



169. European ploughs. The common forms in use in Eu- 

 rope and America are : (i) the Swing Plough, (2) the Wheel 

 Plough, (3) the Double Furrow Plough, (4) the Three-Furrow 

 Plough, (5) the Paring Plough, (6) the Subsoil Plough, (7) the 

 Subsoil-stirrer or Subsoiler, (8) the Ridging or Double-mould- 

 board Plough, (9) the Pulverising Plough, (10) the One-way 



