Corduroy Roads. In timbered country, where roads must pass over wet and muddy places, corduroy roads are sometimes employed. They are built by laying logs side by side across the roadway. By taking sufficient care in construction to select the logs and even up the spaces between them with smaller pieces, a reasonably smooth road may be built. Roads of this kind are at best very rough affairs, and require a great deal of work to keep them in fair condition for travel. They are of value only as temporary roads across bad places where the cost of a better road would be too great.
Plank Roads. Many of the old toll roads in some parts of the country were plank roads, and at one time they were quite common. They are now rarely con structed.. The road is built of planks 2 to 4 inches thick and 8 or 9 feet long, laid upon two rows of stringers about 5 feet apart. The ends of the planks are not in line but are stepped off to assist wagons in passing from the side upon them. Usually a single line was used and teams turned out upon the earth road at the side in passing; but sometimes a double track was provided for teams in each direction. When in good condition, roads of this kind may be very good for travel, but they very quickly get out of repair and are not economical.
Shell roads. In some localities where oyster shells are plentiful, these are used in constructing roads. They make a road very similar to that built of a soft limestone. The road is constructed in the same manner as with gravel, the shells being readily com pacted by the traffic, and binding well in the road. The material is too soft to resist the wear of heavy traffic, and grinds up rapidly under travel. For localities where traffic is not heavy and a harder road covering would be expensive, these roads have often been found satisfactory and economical.
• Burnt-Clay Roads. In certain districts in the Southern states, sedimentary clays very commonly occur, and other road materials are not available. It has been proposed to form a road surface by burning the clay, and experiments have been made by the United States Office of Public Roads which seem to indicate that in many instances this may prove an effective means of road improvement in such localities.
* After grading the road to an even width between ditches, it is plowed up as deeply as practicable. it will be found necessary to use four horses or mules, as the extremely heavy nature of the clay makes the work of deep plowing difficult. After the plowing has been completed, furrows are dug across the road from ditch to ditch, extending through and beyond the width to be burned. If it is intended to burn 12 feet of roadway, the transverse furrows should be 16 feet long, so as to extend 2 feet on each side beyond the width of the final roadway. Across the ridges formed by these furrows — which should be about 4 feet apart — the first course of cord wood is ' laid longitudinally so as to form a series of flues in which the firing is started. From 15 to 20 of these flues are fired at one time.
"The best and soundest cord wood is selected for this course and should be laid so that the pieces will touch, thus forming a floor. Another layer of wood is thrown irregularly across this floor, in crib formation, with spaces left between in which the lumps of clay are piled. Care should be taken that the clay placed on this cribbed floor is in lumps coarse enough to allow a draft for easy combustion.
"After the lumps of clay have been heaped upon this floor, another course of wood is laid parallel to the first. The third layer is laid in exactly the same manner as the first, and each opening and crack should be filled with brush, chips, bark, small sticks, or any other combustible material. The top layer of clay is placed over all and the finer portions of the material are heaped the whole structure. A careful arrangement of this cord wood cribbing to separate the clay is impor tant, and the directions should be carefully followed.