all seasons of the year whenever it was deemed to be beneficial, and to contract with the adjoining land owners for this work at a rate of from 75 cents to $1.00 per mile, not less than 20 feet wide, for each time the road was dragged, the higher price to be paid for work done during the months of December, January, February, or March. The law also provides it to be unlawful to place loose earth, weeds, sods, or other vegetable matter on a road which has been dragged without the authority of the road officials; to place any material which will prevent the free flow of water; for any traffic to pass over a surface just dragged until same shall have partially dried out or have frozen, except in those instances where the road is not sufficiently wide to provide a safe by-pass or on roads wide enough so that the wheels will not make a rut nearer than 9 feet to the center of the dragged portion.

In order that all commissioners should follow the same practice, the following instructions were published:

"Roads properly dragged will dry out weeks earlier in the spring than a road not so maintained, and when dried out will be smooth and in excellent condition. Moreover, they will not rut up so readily during the winter. The ordinary country road can be well maintained if dragged at the proper time on an average of twice a month. The dragging will have to be more frequent during winter and spring than in the summer time.

"Unless the road is in the right condition, the work of dragging will be wasted. One thing to be insisted upon is that the work be done at the right moment. The right time is when the road is wet. The muddier it is the better the results. On a road that is in extremely bad condition where the mud is very deep, it is probable that the lap-plank drag can be worked to better advantage. In the summer time and early fall, dragging should be done while it is actually raining, for unless the rain is exceptionally heavy and long continued, the water will penetrate the dry roadbed so fast that the surface will be comparatively dry when the drag is used after the rain has stopped, with the result that the road surface will work up in crumbs. When this happens it is a sign the road is too dry. The nearer it is

possible to spread the mud over the road as a mortar, much in the same way a mason works mortar with a trowel, the greater the improvement produced. Under no conditions should a road be dragged when it is dry. This merely crumbles up the surface and makes a layer of the loose material which quickly becomes dust and is again turned into mud, which will hold water on the surface of the road; and this is exactly the condition that is to be prevented. Drag when the road is good and muddy. Don't drag when it is dry. Drag whenever possible at all seasons of the year. If a road is dragged immediately before a cold spell it will freeze in a smooth condition."

CHAPTER VIII

GRAVEL ROADS

Statistics gathered by the U. S. Office of Public Roads from road officials in various parts of the country show that there were approximately 103,000 miles of gravel roads in the United States in 1909, which is about double the amount improved with broken stone. There are many localities throughout the Middle West that are devoid of road-building stone, but are fortunate in having good gravel deposits.

THE GRAVEL

FORMATION AND OCCURRENCE. The formation and occurrence of gravel deposits have been previously discussed in Chapter VI.

REQUISITES OF GRAVEL. A gravel to make a good roadbuilding material should be composed of stones that will not readily disintegrate under traffic; that vary from a large to a small size, the proportion of the different sizes being such that the voids will be a minimum; that contain enough binding material to fill the remaining voids and cement the whole mass together.

As a general rule a bank gravel is better than a stream gravel, since it contains more fine material which will act as a binder. River gravel contains more silica than a bank gravel of the same locality, since the clay is more readily washed out. A gravel which contains too much fine material may be improved by screening, while one which is lacking in binding material can be improved by adding some cementing material such as clay, shale, marl, loam, or stone screenings. An indication of the binding qualities of a gravel may be obtained by noticing the gravel in the bank. Usually if the bank faces are vertical, and

a pick is required to dislodge the gravel and large chunks may be broken out in which the smaller pebbles are firmly cemented together, the gravel will make a satisfactory road material.

The Binder. Frequently a mistake is made in selecting a gravel that will pack quickly, and as a result a gravel is used that contains an excess of clay, which is the most common form of binder that naturally occurs in gravels. An excess of 20 percent of clay in the mass will produce mud during a continued wet spell. Just enough clay to coat the pebbles without having any free lumps would be an ideal gravel. To remove an excess of clay, the gravel must be screened and sometimes washing will have to be resorted to. Iron oxide has been mentioned as one of the cementing materials found in some gravels, occurring as a slight coating on the pebbles. Gravels of this nature make an excellent road material and sometimes compact much more firmly in the road under traffic than in the original bed. The gravels from Paducah, Kentucky, and from Shark River deposits in New Jersey are examples of this type. Similar deposits, in which there is little or no clay present, are found where the cementing material is a lime or a combination of lime and iron ore. Enough small pebbles are sometimes present, which will crush up during the construction of the road or under the action of traffic and will furnish a binder that firmly cements the larger stones together. Loam and finely divided silica also compose the binding material in some deposits.

Specifications. The Michigan State Highway Department's specifications require that the gravel for the first course shall be good clean bank gravel, of which not less than 60 percent by weight shall be pebbles that will be retained on a screen of 1/8-inch mess and pass through a screen having 21⁄2-inch holes. The gravel for the top course must be the same, except that no pebbles are allowed in this course too large to pass through a screen of 12-inch holes and that not more than 20 percent of the mass shall be clay uniformly mixed and with no free lumps.

The 1912 specifications of the New York State Highway

Department require that a cementatious Hudson River gravel shall be used, equal in quality to Peekskill gravel; that the gravel for the bottom course shall consist of gravel varying in size from 3 inches to 11⁄2 inches, with just a sufficient amount of fine material to fill the voids; that the gravel for the top course shall consist of gravel varying in size from 11⁄2 inches to fine. The specifications of Hennepin County, Minnesota, with regard to the gravel read as follows:

'Acceptable material will consist of 75 percent of clean coarse gravel varying in size from 8 inch to 11⁄2 inches with 15 percent of clay and 10 percent of sand, the latter ingredients to be well mixed in mass.

"No sod, vegetable soil, or any foreign matter will be allowed, and care must be taken that strippings be not mixed with the gravel.

"A larger percentage of sand may be permitted on clay roads or a larger percentage of clay on sandy roads, to be approved by the engineer, if the excess be deposited uniformly on the subgrade."

Specifications for road gravel in 1912 to be furnished by the parks and parkways in the Borough of Brooklyn, New York, were as follows:

The Hudson River road gravel required shall be what is known as 'double screened' and 'fine' gravel. It shall be free from all foreign substances and meet the following requirements.

"Double Screened Gravel. Percentage of wear not to exceed 5 percent.

Percentage of voids not to exceed 45 percent.

Cementation test by method U. S. Department of Agriculture to be not less than 25.

Percentage retained on 11⁄2-inch screen not to exceed 10 percent, nor be less than 5 percent.

Percentage retained on 3-inch screen to be not less than 75

percent.

Fine Gravel. Percentage of substances soluble in water not to exceed 5 percent.