No filling should be brought up in layers exceeding nine inches in depth. During the rolling, sprinkling should be attended to wherever the character of the soil requires such aid. The cross section of the roadway must be maintained during the last rolling stage by the addition of earth as needed. On clay soils a layer of sand, gravel, or ashes spread on the roadway will prevent the sticking of the clay to the roller. As previously explained, the finishing touches to the road surface should be given by a heavy roller. Before the earth road is opened to traffic, deep and wide side ditches should be constructed, with a fall throughout their entire length of at least one in one hundred and twenty. They should be cleaned and left with the drain tiling connections, if any, in good working order. Clay soils, as a rule, absorb water quite freely and soften when saturated, but water does not readily pass through them; hence they are not easily subdrained. When used alone, clay is the least desirable of all road materials, but roads constructed over clay soils may be treated with sand or small gravel, from which a comparatively hard and compact mass is formed which is nearly impervious to water. Material of this character found in the natural state, commonly known as hardpan, makes, when properly applied, a very solid and durable surface. In soil composed of a mixture of sand, gravel, and clay, all that is necessary to make a good road of its kind is to "crown" the surface, keep the ruts and hollows filled, and the ditches open and free. [Illustration: Sand Clay Road in Richland County, South Carolina [_Sand soil with nine inches of clay and two inches cover of sand_]] Roads are prone to wear in ruts, and when hollows and ruts begin to make their appearance on the surface of an earth road great care should be used in selecting new material, with which they should be immediately filled, because a hole which could have been filled at first with a shovel full of material would soon need a cart full. It should, if possible, be of a gravelly nature, entirely free from vegetable earth, muck, or mold. Sod or turf should not be placed on the surface, neither should the surface be renewed by throwing upon it the worn-out material from the gutters alongside. The last injunction, if rightly observed and the proper remedy applied, would doubtless put an end to the deplorable condition of thousands of miles of earth roads in the United States.