proper proportions in each respective case will be most readily and satisfactorily determined by experimenting with a number of samples, say a cart load of each, in different proportions, which should be carefully noted, all being placed contiguously on the road-bed where they will be equally exposed to wet and to use. A few months' experience, under such test of the various mixtures, will give the road maker data which theory cannot furnish.

In some sections of great area no other material than clay can be obtained; hence it must be used as road material in its natural state. The general principles involved in the construction of gravel, loam, and other roads, and described under those heads, are to be observed in constructing a road exclusively of clay; the gutters, how. ever, should be made as deep as is practicable, and the road-bed as narrow as the travel will admit, and be as highly crowned as is admissible, thus guarding against absorption of water from the gutters, and effectually shedding the rain-fall from the bed. There is no material in the catalogue treated that forms so perfect and delightful a road for pleasuredriving as clay, when in a certain condition; but it is so difficult to be maintained in the desired state that it is judicious to incorporate sand or gravel with it, wherever practicable.

There are districts of country many miles in extent, where nothing but drifting sand can be obtained for making roads. Where the depth of the sand is great before reaching a tenacious subsoil, a road-bed of sand will be more compact and better, if made lower than the surface of the land on either margin, so that water may flow on to, instead of being drained off from, the road. Like clay, pure sand is not a desirable oad material, and quicksands, not unfrequently found in extensive sandy regions, are dangerous. Where drainage of quicksands is impracticable, two thicknesses of planking laid over the place to be crossed, the lower planks running in the direction of the road, and the upper ones across it, have been found to answer very well as a sort of a floatingroad. A contractor on the Knox and Lincoln railroad in Maine has recently encountered a quicksand into which he has sunk pile upon pile to the depth of one hundred and forty feet, and no indications of a hard substratum are yet apparent.

PLANK ROADS.

Plank roads have been so universally unsatisfactory that valuable space need not be occupied with directions for their construction.

I. A. Lewis, of Howard County, Missouri, says that a plank road was constructed in that county twenty-six miles in length, costing $100,000; but it has long since been abandoned. Numerous instances may be cited of their failure from all parts of the country, but not one in which they have been a success. A plank road is a good road when in proper condition, and may be a necessary kind in some districts of the country; hence it may be well to state that it is claimed that, by steaming the plank, and charging them with creosote, costing about eight dollars per thousand feet, board measure, their durability will be doubled.

THE LONGITUDINAL GRADE FOR A ROAD.

There is perhaps no branch of the subject under consideration which demands more attention by the engineer than that of the reduction of road grades to the minimum under all practicable circumstances. We can better afford to increase the length of a road considerably than to

retain grades, in places, so heavy that a team is unable to haul more than half, or perhaps one-quarter, the load it can on all the remainder of it. Roads which are steep in the line of their axis are not only more severe on teams, but they are dangerous, and much more expensive to keep in repair. Various opinions have been expressed by engineers and essayists on this subject. Mr. H. F. French, of Boston, Massachusetts, in a very able paper on roads, contained in the report of this Department for 1866, says: "In view of every consideration, except drainage, the level line is probably the best; but, as drainage is essential, and, as will be seen when we come to consider the construction of roads, it is desirable to make them as flat as possible transversely, a slight slope in the length of them is found expedient. This slope should be one in two hundred, which is sufficient for drainage without injury by washing, and adds little to the draught."

A grade of one in two hundred is a very desirable one, so far as draught is concerned, but it is nearer level than is practicable on any considerable proportion of our country roads; and, as regards drainage, it will be of little service. Much lateral slope is objectionable, but we do not consider that a slope of one-quarter of an inch to one foot is so, while it is sufficient to provide lateral drainage, which is more efficient than longitudinal drainage. The widest track of country wagons does not exceed five feet, and, with a slope of one quarter of an inch to one foot, the difference in the height of the wheels when the vehicle is on the side of the road, is but one and a quarter inch, and this is reversed in returning. It often occurs in rural districts that it is practicable to drive a large proportion of the distance on the summit of the road bed, where the vehicle will be on a level. It is next to impossible to prevent road surfaces from rutting to some extent, and a "slope of one in two hundred" only, while it is so gentle that there will be no tendency to wash, will certainly keep surface water on the road-bed so long that much of it will be absorbed, which may be avoided in lateral drainage, without injury to vehicles, displacement of lading, or inconvenience to passengers. It is not practicable to give a rule for the exact amount of longitudinal grade of roads, as they are affected by so many circumstances. Primarily the best provision for business traffic should be considered paramount to all else, yet this has often to be modified by local circumstances, whether in regrading old roads or in locating new ones. In the latter, if the locality is mainly unsettled, and the probabilities are that the building sites will be most popular near the summits along the line of the projected road, the engineer should prospect contiguous lands, and so modify the route that the necessary laterals may connect with the road by grades that shall be easy, safe, and inexpensive.

There has been a very general and striking change in the taste evinced in locating rural homes, country seats, and faim buildings, of late, to provide for which a corresponding change in the roads by which they are to be reached has become indispensable. Formerly, the popular site for rural buildings was under the lee of elevated ranges of land, near the streams, or springs at the base of hills, to accommodate which the public roads generally traversed the banks of streams, in which position the drainage of all the high lands must pass under or over them. The advantages of the modern system are numerous, and the disadvan tages few. The salubrity of the high sites, the more extensive and pleasant view secured from the buildings, as well as from the summit or the hill-side road by which the buildings are reached, the reduction of cost of construction and maintenance of such roads, the superiority of the grade generally obtainable, as compared with those along the streams,

and the greater feasibility of securing dryness about the buildings, as well as of beautifying the landscape in their vicinity, are among the most prominent advantages of the modern selections over the primitive. Some have urged as objections to the high sites, that they are bleak and cold, and that water is not convenient. The former objection is fully met in the modern improved methods of building, and of economically generating and circulating heat; while, by the use of improved hydraulic apparatus, the supply of water is made ample, and luxuries unknown in the old system are fully enjoyed.

Where objectionable grades, say of ten feet to one hundred, the heav iest that should ever be tolerated, are unavoidable, the following instructions for construction and repair should be observed: Avoid short curves in the road; make the bed wider on the hills than on the plains, and especially in the curves. If the road runs along the side of a slope, grade the surface of the bed, so that all water falling on it shall be cast to the gutter on the upper side, as there is great danger of accident in icy times, if any portion of the bed has a lateral slope with the hillside. On such road provide low water bars across the road at intervals of thirty to forty feet. These bars should be placed obliquely, and should discharge all the water in the gutter on the upper side. If the gutter is disposed to wash, it should be paved, and the curb of the pavement on the road side set so low that water from the road-bed may flow into the gutter the entire distance from bar to bar, instead of being required, as is frequently the case, to flow in the ruts of the road-bed until it reaches the bar, which it often overflows and washes away continuing to flow on the road until dangerous gullies are cut, requiring much expense to repair them. If the hill is long, say one-fourth to half a mile, the water should be carried across the road in culverts, one hundred to one hundred and fifty feet apart. The best and cheapest common road culvert may be made of hard-burned terra cotta pipes. On hilly roads they are rarely required of more than eight to ten inches caliber. These pipes need no sleeves, or bells, nor any cementing of the joints; and are less expensive than the common stone culvert, even where the stones are at hand. The capacity of the pipes, owing to the smoothness of their interior surface, is much greater than that of a stone culvert of the same area of cross section. The pipes should be burned like hard, red brick, and are then as durable as granite. The pipe culvert should receive the water from a shallow well, walled up with stones or bricks. This well should be in the line of the gutter on the upper side of the road. The water from the gutter should fall into the well over a flag on the wall of the well, and between two side walls, carried up with the other walls to a height sufficient for a proper opening, when the well and the opening in the upper side should be covered with a strong flag. This flag should overlap the inner face of the wall of the well at the opening, at least one foot, that animals may not step into the well. This arrangement makes the upper end of the culvert sightly, secure, and free from all dangerous effects. The trench in which the pipes are laid should have a fall, so that the water from the culvert may be discharged upon a natural surface, as it will be less liable to gully it than an artificial bank.

STONES ON EARTH AND GRAVEL ROADS.

In preparing earth and gravel road-beds, all small stones, down to half the size of a hen's egg, should be removed from the surface soil, as the tendency is for them constantly to work up to the surface, where they are injurious to the feet of the horses, and to vehicles, wear and