cost of the work to be executed. He should be authorized to purchase all teams, vehicles and implements required, the same to be the property of the county, and to employ as many competent foremen as required for his district. They should have charge of these teams, &c., and have power to employ, control and discharge the number of laborers directed to be employed by the engineer. The foremen should each have their respective districts allotted them to be kept in repair. The engineer and his foremen and the laborers employed should be required to devote their entire time to labor on the roads. The water bars, culverts, bridges, and gutters should be examined as often as once a week, aud all loose stones, and other surface obstructions removed. Work for repair of surfaces should be constantly pursued, and the principal amount of material required on the earth roads should be applied in the dry season. The winter should be devoted to quarrying stones for bridges, culverts, and macadamizing, and in raising and hauling gravel, and depositing it where it may be readily applied at the proper season. With such a force in charge of the roads the amount and quality of work executed would be more than double, and the actual tax required less than under the prevailing system.

COST OF ROADS AND EXPENSES OF REPAIRS.

According to all the returns from different States, the average cost of construction of gravel roads is $2,241 per mile, and the average annual cost per mile for repairs is $103. It appears, from the reports, that only a very few of the roads are improved by a gravel bed, and neither the width of the beds so improved nor the quantity of material applied is given. We may reasonably infer, however, that neither is greater than is absolutely required, and yet we find the cost of construction per mile to range from $700 to $4,000, and to average $2,241. The annual outlay per mile varies from $4 to $200, the average being as above stated, $103.

By reference to the table showing the cost of repairs to common roads per mile throughout the country, we find it to vary from $1 to $59, and the general average is $18 11 per mile.

The returns show that the average cost of construction of macadmized roads per mile is $3,290, and it varies in the different States from $500 to $6,336. The average annual cost per mile for repairs of macadamized roads, as reported, is $40, varying from $10 to $100 per mile. The average cost of construction of plank roads per mile is reported to be $3,000, and the average annual cost of repairs per mile is $550. The following, table, compiled from replies to circular issued by the Department, shows the average annual cost per mile of repairs of common roads in the respective States:

BRIDGES.

The writer has observed in various parts of the country common errors in bridge construction, which he proposes to notice, with remedial suggestions. At the present comparative prices of wood, stone and iron in all districts, except perhaps on extensive prairies, where the former two are very scarce, wood and stone are considered so much cheaper than iron that they are generally used. Where good quarry stones and suitable sand and lime or cement are conveniently attainable, the span required not more than thirty feet, rock foundations for the abutments within reasonable depth, and the banks of a proper height, the stone arch with stone parapets is, perhaps, as economical a structure as can be adopted. Where greater spans are required, and the banks are low, stone abutments and well constructed frame covered bridges are prefer able. Not a doubt exists of the economy of siding and roofing wooden bridges, and of extending both over the abutments, so as to effectually protect from rain the timbers and planking at these points, as they are known to decay first when not protected. There is a frame covered bridge in Harford County, Maryland, which was built more than fifty years since, and is still safe.

Among the errors in bridge construction, those most common are the injudicious distribution of material, particularly of timber; the contraction of the water way, so as to expose the superstructure to liability to be swept from the abutments; neglecting to bolt the superstructure to the abutments; laying the flooring with close joints, instead of with proper openings, to prevent water from standing on the floors; using perishable varieties of timber, and even allowing the sapwood to be used in part, by which all is reduced to its ephemeral character. No error is perhaps more common, and none results in so needless and speedy destruction of the longitudinal timbers of bridges, as the want of attention to keeping them dry, where they rest on the abutments, and especially at the ends where they support the earth-filling of the road-bed.

The durability of the timbers may be increased by introducing a light back sill and short light joist about two feet in length, with a plank on edge resting against them, to support the filling independent of the main, horizontal timbers, that air may circulate around the ends; and by covering the ends of all timbers resting on abutments and piers with several thickness of tarred paper, these being the points where decay often destroys when the other parts are unaffected.

MINERAL FERTILIZERS OF THE ATLANTIC

STATES.

The economy and necessity of the use of mineral fertilizers have been so long admitted and are now so generally appreciated that it is deemed sufficient, in the limits of this article, to state the locality, extent, and nature of the wide-spread and liberal deposits of mineral manures in the Atlantic States, with some analyses, and such statistics as are attainable, showing their accessibility and cost.

Fertilization, in its widest sense, includes two processes: 1st, supplying the soil with materials intended to furnish plant food, either directly or by rendering available substances already present; 2d, the addition of matter for its physical effect merely; the former method is chemical, the latter mechanical, fertilization. Lime and greensand are examples, among mineral agents, of the first class; sand and clay of the second.

The elements supplied to the plant by mineral fertilizers are (omitting the least important, and those existing in the vegetable but in extremely minute quantities) lime, soda, potash, and acids of phosphorus and sulphur. Fertilizers of this class, then, generally speaking, will include all minerals capable of supplying these materials, either with or without chemical or mechanical preparation prior to admixture with the soil. Practically, however, the number of substances used is determined by the ingredients needed by the plants cultivated and lacking in soils, and the expense of obtaining them and reducing them to a form easily assimilable by the vegetable.

Lime constitutes the base of all the important fertilizers of this class in the United States, excepting the greensand marls, of which the New Jersey formation is the type, in which the percentage of lime is so small that it may practically be left out of consideration.

Limestone, or natural stratified carbonate of lime, in all its varieties, is available for agricultural purposes wherever it can be economically mined and prepared. This preparation consists essentially in the reduction of the stone to a finely comminuted state, which is usually accomplished by burning. In districts where fuel is scarce and water-power at hand, stamping or grinding may be found more economical, though the product will be slower in its action; and, lacking the causticity of burned lime, will not aid so effectually in the decomposition of organic

matter.

Admixture of magnesia with lime is not now, as once, believed to be injurious to the fertilizing power of the latter. Dolomites and dolomitic limestones accordingly find a place among mineral manures; but, from their composition, are necessarily less efficient than the purer limestones.

Sulphate of lime, gypsum or plaster, has a well-established and high rank among fertilizing agents, furnishing to the soil sulphuric acid, in a readily assimilable form, as well as lime; and, though not widely disseminated, exists in large quantities, so as to be cheaply obtainable at most points.

Phosphate of lime is found in many natural forms. The shell beds, sands, and marls contain it; and one or two veins of almost pure apatité have been opened. The fossil excrement of marine animals, known as

coprolites, is very rich in phosphate of lime; and, although not found in great mass in the United States, forins an important part of many of the richest marls of the south. By far the most important source of this material, however, is the recently discovered deposit of South Carolina. While lime may be considered the base of this fertilizer, undoubtedly its most important ingredient is its phosphoric acid.

The term "marl" having so many and such different significations, dependent upon local usages, as well as the various classifications of scientific geologists, it is highly desirable that it should be limited to some specific fertilizing material or class of materials, rather than, as now, be made to include deposits as far apart in their chemical constitution and value as in their period of formation. At least, when used, it should be so qualified as to indicate the mineral species to which the substance belongs.

The marls of the United States may be divided into argillaceous, glauconitic or greensand, and calcareous. Argillaceous marls are of comparatively little agricultural value, if we consider their chemical constitution only, consisting mainly of clay and sand, with a trifling percentage of lime. There are circumstances, however, as before alluded to, in which they may become true and valuable fertilizers. Glauconitic marls include the greensands of New Jersey, Delaware, and Maryland, and a few localities further south. They are dependent, for their power of permanent beneficial action, upon the potash and phosphoric acid they contain. Full analyses of these deposits will be found in the report of the chemist.

Calcareous marls are the débris of countless successive generations of life, the remains of which may or may not be recognizable, according to the amount of pulverization and attrition they have undergone from the motion of the water in which they were deposited, and the subse quent conditions to which they have been exposed. These deposits range in time from the cretaceous epoch of geologists to the present era, and are even now in process of formation both in marine and inland waters. They are found in greatest amount in the tertiary strata.

The foregoing account of the origin of marl applies with equal force to most of the limestones. Marls, however, are generally understood to be friable to a considerable extent, and this, together with the fact that many of the marls retain a sensible proportion of organic matter, constitutes a line of distinction between the two. This line is one, however, often hard to draw; for, if it is true that even the hard and crystalline limestones are but the result of various forces, as heat and pres sure, acting upon sedimentary strata containing organic remains, it is evident that there may be all grades of consolidation and homogeneity according to circumstances.

The physical character of calcareous marls varies with the class of animals, remains of which form their active ingredient, and the state of preservation of the latter; and their agricultural value varies with the proportion of inert matter they contain, and which frequently forms a matrix for the shells and other organic formations.

The deposits known as pond marl, or sometimes as shell marl, found in our lakes and ponds, or upon their former sites, and often under peat, explain, by their formation, which may be watched in all stages, the mode of origin of the greater part of the calcareous group. Water containing carbonic acid is, under pressure, a solvent of carbonate of lime, from which the microscopic testaceous animals inhabiting such water, by absorption and secretion, form their shells; and, dying, these are de posited, either to accumulate in vast masses, or, if the water is not