THESIS eyed ECONOMICS is BROAD BU! Se ie1e if HIRD ATE ain a FRANK FF -r ROGER a GERS THESI§ 22 / 9 ? om a ’ oa : ee te ee a eon eee 9 Ke Tm wee wos “- . 4 - oe . ‘ (fo. ECONOMICS OF ROAD BUILDING ESPECIALLY APPLIED TO MICHIGAN Evolution of the Wheel. At the dawn of history our ancestors were moving about in caravans, driving their flocks and transporting their goods on the backs of m6n and beasts. Those peoples fortu- nate enough to have located by streams and seas immediately devised rude water-craft. That the sledge was in use by the early Egyptians is clearly proven by carvings on ancient monuments; and that rollers were used under the massive blocks of stone as they were moved into place to form the great pyramids can scarce- ly be doubted. It was but another step to put rollers under the sledge and thus form a rude wheeled vehicle with rotat- ing axle. Later solid wheels were cut off the ends of logs and placed on rigid axles. But that the built up wheel is also verg old is attested by such words as "nave", "felloe" and"tire" in both the Bible and the writings of Homer. The earliest Ghariots ere two whéGled vehicles with open backs used for war, state purposes and hunting, but rarely as a conveyance. When the Romans conquered Britian they found a chariot with high wheels and a seat which so pleased Cicero that he requested that one be sent to Rome for a pattern. With the development of wheeled vehicles, and the ad- vancing needs of society the trail, always the first means of THESIS ius. communication in a new country, gave way to tracks and road- ways over which such vehicles could be drawn. The Roman Roads. While the Romans were the foremost road builders of antiquity every notion that has been noted for progress has been a nation of road builders. Indeed the Roman roads, which extended from the wall of Antonius in Britaan to the limits of the empire on the Euphrates, were so subdstantial- ly constructed that in many places they are the most lasting reminders of Roman conquest. The prime object of these roads was military, and they were not especially built for wheeled vehicles. They were built by enslaved labor regardless of expense, and in the most direct lines regardless of grades between the places joined. It has been estimated that they cost fifty million dollars a mile. They have survived the eeyages of time more because of their massivemess than because of the engine®ring Skill displayed in their construction, though the latter was not wanting in many particulars.. They were,in fact, almost continuous walls of masonry about three feet deep and the full width of the traveled way. Near the cities more pains were taken and the surface was paved with hexagonal stones blocks, well trimmed and so carefully fitted that even today it is difficult to locate the joints. The center of the roadway was the highest and on the sides were gutters to carry off the water. Where the road LO846¢ b traversed flat countries the gutters became ditches, thus complying with modern requirements for road drainage. Modern Roads of Europe. With the deline of the Roman Empire thetr roads fell out of repair and gradually out of use. It was not until 1764 that Trodguot, a French Engineer, vegan to construct roads, upon more scientific principles, using small fragments of broken stone placed upon a well sheped bed of larger stones set on edge. Similar roads were intpyoduced into England by Telford in 1824, and to this day roads so constructed are designated by his name. The macadam roads of Europe began to be built rapidly in the first quarter of last century. It was in 1816 that John L. Macadam, then Surveyor General of the Bristol dis- trict, began the Construction of a system of broken stone roads which soon covered England and became, for a time, the finest roads of Europe. So fast did the work progress that it is estimated that, at the time of Macadam's death in 1836, there were not more than two hundred fifty miles out of a total of twenty-five thousand six hundred miles or road in the kingdom that had not been thus paved. The famous roads of England and France were all built in the years just prior to the development of the railroad, the latter being promoted by the First Napoleon entirely as & War measure, yet they contributed in a great degree to the rapid social and commercial development of both countries. Early Rmerican Roads. During these years the United States was not idle, and not less than fourteen millions of dollars was appropriated by congress previous to 1830 for the building of trunk line highways to penetrate the undeveloped west. The results were such undertakings as the National Road extending from Cumberland, Maryland westerly, passing through Southwestern Pennsylvania, Central Ohio and Indiana, St. Louis, Missouri being the objective point, but which was never reached. Some seven million. dollars was expended on this road alone. The "Wilderness Turnpike", a toll road aided by the government, formed a Similar highway across Central Kentucky and facilitated migration from the Virginia settlement west- ward. State Aided Roads. With the development of the railroads national aid for highways ceased, and not until within the last two decades did the recent awakening to the economic value of well con- structed highways attract general attention. This time it was taken up by individual states, although the government promptly established a Bureau of Public Roads in the depart- ment of Agriculture which aids in the building of object lesson roads and tests road materials free of charge. As the cost of constructing first class gravel and macad- am roads is considered too great for individual counties and townships to undertake unaided, twanty-two states in the Union are now rendering some form of assistance. Thirteen of these are giving cash, two are furnishing convict pre- pared materials, one furnishes the state prisoners free to work on the roads under certain restrictions, while the others are, at present, serving only in an advisory capacity. States giving money aid vary considerably in the amounts given. In New Jersey the state pays thirty-three and one- third per cent, the county fifty-six and two-thirds per cent and the township ten per cent of the cost. In Massachusetts the state pays seventy-five per cent and the county twenty- five per cent of the cost. In Connecticut the state pays from two-thirds to three- Sourths of the entire cost, the towns paying the remainder. The smalle#@® sum is paid only where the town is valued at one million dollars or less. In New York the state pays fifty per cent of the cost, the county thirty-five per cent and the township fifteen per cent. Michigan's plan is more simple. }re#s in which L equals load; f equals tractive force; r equals 14 road resistance; s equals sine of angle of incline. In Michigan the maximum grades for roads on which state reward is paid is limited to six per cent- No other state has placed a limit, the officers in charge having it at their discretion. ' Gillette says, "The tractive power of a horse is great- er than authorities state and that a team can readily exert four times as much tractive energy going up short hills as the avergge pull on a level". As Gillette's observations are based on the actual use of teams on contract work they should be quite trustworthy. If so no state rewarded road in Michigan will have grddes steep enough to reduce the average loading capacity. Although steeper grades are permissable where actually required, the best practice would keep the maximum down to two or three per cent, the slope of repose for a wagon on first class macadam and gravel road surfaces. A minimum as well as a maximum grade should be kept constant- ly in mind, the former being at least one half per cent, unleas the cost of introducing such grades is practically prohibit- ive. Road surfaces are always maintained at less cost on slight grades than on long level stretches. A level road, crowned sufficiently to shed water to the sides at all seasons, is toosteep for convenient and safe travel. In- deed this very steepness soon defeats its own end by concen- trating the traffic along the apex of the grade, where wheal tracks are soon formed which hold water if longitudinal drain- age is wanting. SENET re: ee 15. Cross Sections. The width of grade, transverse slop and form of ditches should all appear on the plans. In Michigan the law fixes the minimum width of turnpike or grade at eighteen feet. Twenty-four feet is a reasonable maximum. The specifications of the Michigan State Highway Department demand a cross-sect- ion, oval (parabolic) in form, having an averagerese of one inch to the foot from the sides tof the center. The writer advises a slight extra hse at the center to remedy the flat- ness of the parabolic curve. PlateNo. I shows the forms of cross-section recommended by eleven of the leading states now giving state aid. Drainage - Open drains should not be larger than are required to handie the water that naturally flows along the highway. They will necessarily vary in size from the Shallow gutter, formed by a continuation of the transverse slope to the gut- ter bottoms, to the open drain of considerable size. Fre- quently the latter is a previously constructed county drain, so deep that the roadway must be protected by a suitably con- structed guard rail. Tile drains should be used wherever the soil comprising the road bed is springy, or e€ a heavy water bearing clay. The Massachusetts Highway Commissioner reports that, "A sub- grade of sandy loam is the most difficult to know how to treat. Generally speaking, if thirty per cent or more of the material will pads a No. 100 screen, the introduction of at/e drain 16. does no particular good, the carillarity of the soil being so great that it will not give out the ground water". Under drains may be placed under the gutter, in the shoulders, or under the road metal according to the judgment of the engineer, but always oh the side from which the water flows, so as to cut it off before reaching the road bed. For ordinary purposes four inches unglazed land tile are most suitable. In a few cases larger tiles may be required. It is always well to f11l1 over the tile for several inches, if not the full depth of trench, with some porous material like gravel,or cinders, or broken stone, so as to enable the water to reach the tiles more quickly. Earth Roads. Whenever the route of a proposed road is graded and drained in accordance with plans above outlined a well buiit earth road is formed, which will be more or less satisfactory, according to the nature of the soil composing the bed, The cost of grading is in direct proportion to the amount of earth that must be handed and commonly varies from two or three hundred to two or three thousand dollars per mile. For ditching and turnpiking, tre road plows, the flat scraper or Doan scraper, and the four wheeled road machine (scraping grader) are the principal to®ls employed. In the prairie states elevating graders have been used with much success. To make cuts and fills drag scrapers, wheeled scrapers and wagons are used according to length of haul. Plate No-c,platted from Gillette's rules, shows the in- aaaae 7 ARTES E s 7 REREE RRR pe fepeefe , DORRE RETR OR MERE GE és PTET TT es WESAPRPOAT AERA CE SAAR RR ARR RE RRS SERVES CS ME OAD R EUSA POS RAIU SRE R RAE eee PE 17. itial cost, extra cost for each hundred feet of distance that earth is moved and esse the economical lengths of haul for the above named tools. Sand-Clay Roads. In places where gravel and stone are wanting, or the ex- pense of getting them prohibitive, the sand-clay mixture is frequently used for road surfaces to good advantage. It has met with greatest favor in the Atlantic and Gulf states, which, no doubt, is partly due to the mild winters of the south and the absence of freezing and thawing, which dis- integrates and softens our northern soils. It should be noted that the hauling of sand on clay and vice versa, without attempting to obtain the proper mixture, is no building the sand-clay road, and that results obtain- ed by the former method cannot be compared with the results obtained by the latter. There is much difference in the quality ofclays. Clays known as "staking clays" are more easily mixed and usually preferable, but the plastic clays, no doubt, have rather bet- ter binding qualities when the proper mixture is obtained. The amount of clay required in the mixture is approxi- mately the volume of the voids in the sand used. The mix- ture will rarely ever consist of more than one part of clay to three parts sand, and frequently one part of clay to four parts of sand should be used. No doubt the best results WOuld be produced, if the mixture could be made in a pug nmnill,with just the right 18. proportions of sand and clay and the required amount of water. But in practice no such methods can be employed on account of the cost. Clay on Sand. To place the mixture on sand, it is first necessary to grade the road so as to conform to the plans, making very Shallow gutters. It is important, however, that the finished road shall have the regular crown and the gutters a true grade. The bed for receiving the clay can usually be formed by push- ing a part of the sand from the proposed bed to either side with the scraping grader- Upon this bed a layer of clay, not less than four nor more than six inches thick, should be uni- formly spread, rolled sufficiently to crush the lumps ,if there are any, then harrowed until thoroughly pulverized. Immediate- ly after the harrowing three or four inches of sand, which may now be scraped from the sides with the road grader, should be spread uniformly over the clay. The road must then be Sprinkled to saturation or allowed to remain in this con- dition until thoroughly soaked by a heavy rain. When it is wet it mst be thoroughly mixed with such tools as the disc harrow or cut-away, smoothed down and rolled and@if still Sticky, covered with anotheythin layer of sand. If the finished road lacks binding power it is an indication that too much sand has been worked into the clay and more clay will have to be added. If the road covering thus prepared proves too thin, another layer of clay-mixture may be added. Roads built in this manner are giving good satisfaction in several places in Michigan, where the travel is not heavy. 19. Sand 6n Clay Sand can usually be mixed with a clay sub-grade, with less expense, but with somewhat poorer results, owing to ths less perfect drainage offered by the clay foundation. The clay road must be well shaped and drained, having a rather flat cross-section. In this climate quite satisfactory results may be obtained by applying five or six inches of rather course sand tothe clay subgrade, thus allowing it to become mixed with the clay under travel during the wet weather of fall, winter and spring: As the ground becomes settled in the spring the road mst be flatted down with road machines, or other flateing tools, and allowed to go into the summer smooth. Usually two or more applications of sand will be re- quired before desired results are produced. Where this method is considered too slow, tne subgrade Should be loosened before the sand is applied and the sand immediately mixed with the clay by plowing and harrowing, much as described for working the clay into the sand. [n either case plenty of water during the mixing is indispensa- ble. Gravel Roads. Authorities have differed somewhat on the requirements of Buitable road building gravels, most of them, in the writer's opinion, laying too muchstress on the immediate packing quali- ties. Indeed, the average township commissioner, and farmers, generally, have become so imbued with the necessity of secur- \\ 20. ing a gravel that will pack quickly that they have almost lost sight of the fact that the only thing that makes a gravel road better than an earth road is the pebbles-real stones-that it ebtains and is solely dependent upon to bear the traffic and resist wear. Some authorities specify much larger pebbles than have been required by many modern road builders. An attempt to follow such specifications with the general tun of Michigan sravels would make gravel road building so expensive as to be practically prohibitive, and would necessarily discard many whole pits from which excellent roads have beenmade. Gillmore in his "Roads and Pavements", says: "A capital distinction must be made between gravels that will pack under travel amd clean rounded gravel which will not, due to some small proportion of clayey or earthey matter contained in the former, which unites and binds the material together". Recarding size, he says:"Reject gravel for the tcp that passes a one-half inch mesh screen, as being too fine and that which will not pass a one and three-fourths inch screen as being too coarse." But he advises the use of the unscreen- ed gravel for the bottom layer. Byrne in his work on Highway Construction, says : "In selecting gravel the chief quality to be sought for is the Proportyee we giueep of binding." The binding properties he gives as two: "The presence of ferruginous clay, which causes gravel to set or become hard as soon as it is exposed to the atmosphere, and the angular shapes and sizes of the stones". ol. He advises rejecting all pebbles tnat are so large that they will not pass a one and one-half inch screen, also all that are small enough to pass through a threefourths inch screen. He also says that gravel in bottom should be no larger than gravel on the top. A. O. Baker, speaking of gravel in his "Roads and Pave- ments," says: (1) "The fragments should be so hard and tough as not easily to be ground into dust by the impact of wheels and hoofs. (2) The pebbles should be of different sizes, each of the proper proportion. (3) There should be inter- mixed with thecoarser particles some material which will cement and bond the whole into a solid mass®*. Pebbles over two inches in size are held to be too large, but this author does not place a limit for the smaller pebbles. He says further: "That to secure contact at every point all the interstices between the fuagments should be filled. The larger pebbles with smaller pebbles, the smaller pebbles with sand grains, and the sand grains with finer material Called binder. The binder may be clay, loam, silica, stone dust, iron oxide, etc-, or some ingredient which will crush under traffic and supply this dust." In the writer's work as Deputy State Highway Commission- er, directing construction of and inspecting State Reward roads that have been built in Michigan for the past three seasons, the least trouble has been to secure gravels that will consolidate under traffic, and the most difficult task of all has been to secures gravels, without resort to screen- ing, having a large enough content of pebbles to insure a reasonable degree of service. He has yet to find a bank gravel in this state in which the pebbles are all so smooth and clean, and which contains so few lime pebb}jes tnat it will not become reasonably firm under travel sn mn nonths, if =o properly treated. The most common material sougnt for binder is clay, yet, considering all kinds of weatner, it is prcbably the poorest cementing material we have. If present in quantities much in excess of twenty per cent of the mass it makes muddy roads and at best is the most treacherous substance we are sometimes forced to gwse for that purpose. The New Jersey gravels, used in their state aid roads, contain one-fifth their weight of clay. But they are very fine. Of three samples examined by Prof. Baker over fifty per cent passed through a one sixteenth inch mesh screen. Agairfthose roads for the most part are built over sandy soils, and the very fine pebbles which are practically sand, pretty thoroughly negative the bad effects of the clay. In fact, roads built of such gravebs are but a few degrees removed from the typical "sand glay” roads so much used in the gouth and referred to above. It is the clay gravels that always break up in the spring when the frost is coming out, while the gravels that depend on oxide of iron and stone dust for their cementing Qualities are always good, whether the road is wet or dry, frozen or baked in the hot summer sun. Gravels that come from the pit with the pebbles cemented 2S together, even though they contain no clay, will re-consci°diate in the road and become harder than they were in the pit. Tests of a specimen of that kind will always show a lime re- action, and this lime is usually accompanied with iron, due to the fact that water flowing over the lime has a tendency to deposit its iron content. Michigan Gravels. The Bank gravels of Michigan are all of glacial origin and vary quite wicely in their character, both as to the kinds of road of which the pebbles are rounded fragments, and the kinds of earth with which they are mixed. This variation is most marked when the gravels of different sections of the state are compared. The rims of limestone rocks that surround the northern ends of Lakes Huron and Michigan and straits of Mackinac and outcrop at intervals in Menoninee, Delta, Schoolcraft, Mackinac and Chippewa counties of the upper peninsula, and in Alpena, Presque Isle, Cheboygan, Charlevoix and Emmet counties of lower Michigan seem to have materially influenced the gravels in those counties and for some distance shuthward by contributing a large proportion of limestone pebbles. Farther south and in the interior of the state the pebbles represent a larger percentage of ignous rocks, such as granite and trap, also much quartz. It is probable that these came from the harder rocks to the north of Lake Huron, and that considerable percentage of the softer rocks were ground to powéer in transit. The same variation is to a greater extent apparent in the cobble stones or boulder covering these areas. The wearing qualities of the road, after it has been properly consolodated, are almost entirely due to the ability of the pebbles to resist crushing and abrasion, There are few gravels in Michigan that do not contain plenty of limestone pebbles to crush and wear into dust and thus supply all of the fine particles required for binder, leaving the tougher and harder pebbles totiake the actual Wear The best of pebbles are the traps and tougher granites. Quartz pebbles are rather easily crushed into sand, after which they are of little use to the road, for in this con- dition they have practically no cementing value. However, at thgpresent state of road building in Michigan when gravels can be found with or without sereen- ing, containing a sufficient proportion of pebbles which are fragments of good sound rdcks, one must not be too critical as to the kinds of minerals of which they are composed. Finally, if the writer were to sum up the desirable qualities of gravels for: road building in Michigan, he would place them in this order : (1) In direct proportion to the percentage of pebbles (up to about 80 per cent) vonstituting the mass. (2) In direct proportion to the value as road metal of the stones constituting the pebbles. (3) In direct proportion to the value as a cementing material, under all conditions of weather, of the finer particles constituting the filler and binder. The Michigan State Highway Department specifications require that sixy per cent by weight of the gravel shail be coarse enough to be retained on a No. 8 screen; that no pebb}ses shall be used in the bottom layer that will not pass tarough a two and one-half inch mesh screen, and that no pebb}es shall be used in the top layer that will not pass through a one and one-half inch mesh screen. That would seem like a very easy requirement, but it actually rejects more than three-quarters of tne gravels commonly used for road purposes. There are, however, many gravels of a sandy nature from which first class road material could be obtain- ed by screening, and this is being done in some localities. It is almost invariably cheaper to screen local gravels that are witnin a wagon haul of the road than it is to pay freight on gravels from a distance and then havl them from point of delivery to the road. Hand screening is rather expensive. At Mancelona it has cost about forty cents per cubic yard for the screened pro- duct. Gravel has been successfully screened and loaded by horse power. A drag scraper loaded with gravel is drawn up an inclined trackway by means of rope and pulleys, when the gravel is allowed to dump onto a chute screen. The screen Should Ae Bb out six feet long, inclined to an angle of forty five oil oSsis and high enough above the ground, five and one- half to six feet, to per mit the gravel to slide into an ordinary wagon. A suitable screen can be made by using flat bars of 26. steel one-eighth inch by one inch, which are punched, set on edge and rodded together, each bar being separated from the adjacent bars by bolt washers. The bars are then fastened to a frame work made from planks or scantlings. Sometimes round rods, woven together with wires, are used instead of bars. At Millington, Michigan a chute screen, like the one above described but eleven feet long, is placed over storago bins, the gravel being raised to it bg means of an ordinary bucket elevator driven by a 4-H. P. gasoline engine. The bottom of the elevator terminates in a receiving hopper which is depressed so that its top is level with the ground in the bottom of the pit. The top of the hopper is protected with a grating made of roads spaced so as to exciude stones larger than three inches and the gravel is delivered to it with drag Scrapers hauled by single horses. This plant puts out from thirty-five to seventy cubic yards of screened gravel daily, varying according to the amount of waste material (sand) the gravel contains. The cost of screening is said to average about twenty-five cents per cubic yard of screened product , which practically includes the cost of loading, as the storage bins are high enough so that the wagons are driven under chutes and loaded by gravity. The cost of loading by hand would not be less than ten cents'per cubic yard. In some places rotary screens are used in connection with elevators and storage bins Similar to those above described. In these plants water is ffequently used for washing gravels containing clay and loam. Washed gravels are seldom desired for road building. a) ~J Applying the Gravel. Before the gravel is put on the road bed is graded so as to conform to profile and cross-section. Shoulders of common earth or other suitable material are formed on each side of the gravel bed for the purpose of retaining the gravel in position. For single track roads it is important that the contour of the gravel bed shall be parallol to the finished surface, as a uniform depth of gravel is required. See cross- section for Michigan,Plate 1. On double track roads the edges of the metal are often made thinner than the center, when the sub-grade should be formed accordingly. See sections for Massachusetts, Maino and Vermont, Plate l. On soft mealy sand, if the travel is very heavy and a single track road is to be built, it is best to build the shoulders of some bettcr class of earth. Often strippings from the gravel pit can be used at small cost. The writer frequently forms shoulders by putting a row of sods along each margin of the gravel bed, placing them two sods deep and bottom side up. The sand is then scraped up to the sods and substantial and quite satisfactory shoulders formed. Where the sand bed is so mealy that it inclines to mix with the first layer of gravel, especially if the gravel is Clean or of a sandy nature, some binding material must be spread over the sub-grade before the gravel is applied. frequently a layer of clay is placed under the gravel, but this usually works up through the gravel in time and makes a 28. muddy road in wet seasons- Other materials are better. The author has successfully used thin laycrs of marsh hay, rottm straw and coarse horse manure. Pliable woody fibers, such as cedar bark and tan bark, would doubtless serve the same purpose. In Michigan the state reward road law requires that enough gfavel be put on in two laycrs to maxe eight inches of compacted gravel. Experience proves that the packing is about twenty per cent, ten inches of loose gravel being re- quired fo form an eight inch road. It is best to use six inches of loose gravel for the first layer. This gives depth enough sc that it is not readily cut through, and is more economical, in that some- what larger pebbles may be used in the bottom layer. The writer prefers to gage the depth of gravel, the loads all being the same size by calculating the distance that one, two or three loads of gravel, when dumped side by Side, will cover and make the required thickness. Thus, on a nine foot gravel bed two loads of one yard each will cover twelve feet six inches thick, for the first layer and eighteen feet four inches thick for the second layer. A few pegs are set in the shoulders along the margin of the gravel bed the required distances apart and gifted ahead as the work pro- gresses- Then all the foreman has to do is to see that the required number of loads of gravel are evenly spread so as to cover the distance between the stakes. Compacting the Gravel. Immediatehg heavy rolling will not do much to gonsoli- CD CO date a gravel road, and dry rolling is a nuisance rather than a benefit, except to dicover soft spots in the subgrade, which usually have to be corrected by adding mofe gravel, unless the gravel contains eo much material of a clayey nature that it is sure to make a muddy road in wet weather, Experience with gravel roads soon teaches us that gravel will not "come down" under the roller like macadam, but on the contrary re- quires some traffic to properly harden it. In the early stages no compacting tool is so efficient as a spike toothed land harrow, especiaaly one that permit of tilting the teeth backwafds. This harrowing should be- gin with the first layer, as soon as three of four hundred feet of the road has been covered, and kept up every day fhere- after during tee construction unless the road becomes so firm that the harrow teeth make little impression. One or two rounds at a time are sufficient, preferably at noon and night, so as to keep the wheel tracks continually filled. After the first rain that thoroughly saturates the road, or if no rain comes it will be necessary to sprinkle, begin 7% roll, and also to work the harrow all the time the rolling is in progress. At first it is well to yse a land roller, weighted to about two tons, but as the road becomes firmer a heavier roller hastens the packing, and wherever possible a much heavier horse roller or steam roller, wbhighing not over ten tons ,should be used. This treatment applies to each of the courses, and it is impossible to build a first class gravel road without applying the gravel in at least two sepa- 30. ratoup. /avers. Even with the treatment above outlined no gravel road be- cones pe¥fect until it has been traveled for some time, usu- ally not until the second season after it is built. During alYof this formative period it must be carefully looked after and kept free from wheel tracks and hollows. It can usually be kept smooth by means of plank float, the timber or angle iron drag, or sometimes by the skillful use of the road grader. The last named tool, however, often does much damage, by digging up hard places, while the former tools simply shove the loose gravel forward, gradually pushing enough of it to= vards the cneter of the road to preserve the crown, but always depositing it where there is the }east depression. Whenever there is an extra deep wheel track, or evidence of rutting a little new gravel of the best quality should be put on before the floating is done. Repairs . The completed gravel road can be kept in good repair by placing a little good gravel in the hollows immediately after rains, when standing water will point out the least depression. At such times the surface is softer and the new gravel will unite quickly with the old bed. Once or twice a year, spring and fall are the best times, the scraping grader or some other smoothing tool must be used to preserve the crown and fill the central path, which is commonly formed by single horses. Care must be taken so that no earth is scraped onto the gravel. Such treatment will keep a gravel road in good condition until it wears so thin that resurfacing it required. J/ Macadam. It has been said that, "The discovery by Macadam that angular fragments of hard rock, sufficiently reduced in size, will coalesce or bind together into a compacted mass of stone under the pressure of wheels, thus forming a sort of natural mosaic impervious to water; and the system of road making based upon it have been of greater service and bene- fit to mankind than any other contribution to the science of locomotion, except the invention of the steam engine.* In the language of Macadam, a well built road is "an artificial floor forming a strong, smooth, soiled surface, capable of carrying great weight, and over which carriages may pass without impediment.* It is time that Tresaguet had used broken stone on hs roads, but never with out a floor or foundation, and it was left for Macadam to discover that this floor was not necessary He argual that the native soil must bear the weight, no mat- ter what kind of surface was put on it, and that any well drained earth was easily capable of carrying the weight of the paving and the carriages that pass over it. The Massachusetts Highway Coygmission has estimated that non—poraus soils, drained of ground water, at their worst, will support a load of about 4 pounds per square inch; and hav- in mind these figures have adjusted the thickness of their macadam roads to suit the traffic, assuming that on a road built of gragments of broken stone the downward pressure takes an angle of 45 degrees from the horizontal, and is distributed over an area equal to the square of twice the depth of the JF 2 broken stone. Thus if a division of the load in pounds at any po&nt, by the square of twice the depth of the stone gives a quotient of 4 or less » then will the road foundation be safe at all seasons of the year. On sand or gravel the pressure may be safely taken at 20 pounds per square inch. Quality of Stone. A good stone for road building must be hel and tough and the dust, resulting from crushing and the wear of traffic, should have reasonably good cementing qualities. Having the above in mind siz of the most common road building rocks may be arranged in the order of their economic value as follows: $1) trap, (3) Byenite, (3) granite, (4) Schist, (5) gneiss, (6) limestone. Michigan Rocks. In Michigan the most used road stones in order of their value are: trap, cobble-stones, or field bowlders and limes- tone. The former is found in the Upper Peninsula only, and thus far has been little used exoept in the vicinities of Marquette and Calumet.