=Sizes of Stone.=--The stone for the wearing course of a macadam road should be as large as practicable, because the larger the pieces the more durable the surface. If the individual stones are too large it is difficult to secure a smooth surface, and large stones will be readily loosened by tipping as the wheels roll over them. These considerations limit the size to a maximum of that which will pass a 2-1/2-inch screen. Stone of excellent wearing qualities may be somewhat smaller, but never less than that which will just pass a 1-1/2-inch screen. For the lower course, the size is not particularly important except where the earth foundation is such as to require special construction. It is not uncommon to use the same size of stone for both upper and lower course and yet in many instances stone up to that which will just pass a 3-1/2-inch screen is used for the lower course. Stone much smaller in size may also be used successfully, but if the stone is broken to a smaller size than is required, unnecessary expense is incurred. The bonding material is the finer portion of the product of the crusher, which is called screenings. This material may be so finely crushed as to pass a one-fourth inch screen, or may be so coarse as to just pass a one-half inch screen, but in any case must contain all of the dust and fine material produced by the crusher. Where the soil and drainage conditions demand an especially stable foundation course, the Telford type is used. The Telford foundation consists of a layer of stones of various dimensions that can be laid so as to give a thickness of 8 inches. These large stones are placed by hand and therefore the size requirements are not rigid. Stones having one dimension about 8 inches and the others not over 10 or 12 inches are satisfactory. =Earth Work.=--A thoroughly drained and stable earth foundation is essential to success with the macadam type of surface. Before placing the stone, the road must be shaped to the proper cross section and all grade reduction work completed. Preferably heavy fills should have a year to settle before the macadam surface is placed. Side ditches, necessary culverts and tile drains should be constructed as required for drainage. The earth work is often carried out in connection with the construction of the macadam surface, being completed just ahead of the surfacing. In that case, the fills must be carefully rolled as they are placed. The road bed may be shaped in connection with the other earthwork. If the road has been brought to a satisfactory grade some time prior to placing the macadam, the road bed for the broken stone will be prepared as needed for placing the stone.