xvi LIST OF ILLUSTRATIONS 



FIGURE PAGE 



20. The appearance of soil plowed in an over-dry condition . 47 



21. A column of heavy clay showing the cleavages which take 



place upon air drying . . . . . ; . . 55 



22. Map of township in La Fourche Parish, Louisiana, showing 



the way in which the early French Acadian s plotted 

 their farms on the naturally drained margins of the 

 rivers and bayous 59 



23. A 1760-acre unit diked for reclamation . 63 



24. A system of parallel drains 77 



25. A system comprising a main with laterals approaching 



obliquely ......... 78 



26. A system in which the laterals are laid at right angles to the 



main .......... 79 



27. A combination of the systems shown in Figs. 24 and 25 . 80 



28. A system which has been in operation for a number of years 81 



29. A system which has been developed solely by the require- 



ments of the field 82 



30. Showing the way in which the water table is changed by the 



insertion of the tile midway between two others . . 84 



31. Showing how water approaches the tile, when the tiles are 



laid in a rather heavy soil underlaid by a more open 



subsoil ... . . . . - . 85 



32. Economizing in the size of tile ...... 87 



33. Silt-basin built of brick 90 



34. Silt-basin of concrete and sewer tile . . . . .91 



35. Silt-basin built of concrete ....... 92 



36. Drainage level v / . 95 



37. Cheaper forms of drainage or grade levels . .... 96 



38. Leveling rods . . 97 



39. Drainage engineer's leveling rod .... .. > . 98 



40. Target 98 



41. Illustrating how a carpenter's level may be mounted on a 



stand and used for leveling ... . . , . . 105 



42. Illustrating the water level in use . . . . . 106 



43. Closer view of water level and carpenter's level . . .107 



44. Relation of the angle of approach to the distance between 



drains ... ,. . 112 



45. Profile of a portion of field through which a tile drain is to 



be laid . ., .' . 



