tary of War, of March 9, 1872, reporting, at the request of the authorities at Du Luth, the condition of the dike across Superior Bay, was returned to the Secretary of War, with a copy of Major Houston's report of March 25, and the following remarks: "It will be seen that Major Houston is of the opinion that the dike cannot be pronounced complete until after the ice has disappeared and the effects of the spring freshets observed. He recommends that the dike be raised until it shall be in no place less than 3 feet above the present water-level; that the filling be continued as long as any settlement is observed, and that the ends of the dike be connected by earthen embankments with the high ground at each end; the top of the embankment to be 10 feet wide, and of the same height above water as the dike." These views were concurred in, and it was suggested that a copy of this letter and of Colonel Houston's report be sent to the mayor of Du Luth for his information and guidance. Very respectfully, your obedient servant, A. A. HUMPHREYS, Brigadier-General and Chief of Engineers. Hon. W. W. BELKNAP, Secretary of War. CHICAGO HARBOR, ILLINOIS. OFFICE OF THE CHIEF OF ENGINEERS, SIR: I transmit herewith a letter just received at this office from the president of the Illinois Central Railroad Company, asking that instructions be given the United States district attorney to relieve that company from the injunction now in force at the instance of the Secretary of War, so as to enable it to commence the construction of docks in the outer harbor at Chicago north of Randolph street. Though no specific declaration has been made in behalf of the railroad company of its acceptance of the limiting harbor or dock lines proposed by the board of engineers convened in Chicago in September last, (a copy of the report of the board, with your approval of its report and plan, was sent to the president of the company October 7,) it is inferred that the company intend to conform to the approved plans of the War Department in building their docks. In the printed statement in relation to docks and wharves in the outer harbor of Chicago, submitted by the president of the Illinois Central Railroad Company to the Secretary of War, July 25, 1871, the following language occurs, viz: "How far these docks shall extend out into the harbor is a question which it [the company] is desirous to have settled. In this respect the company has no plan which may not be modified, and which will not be cheerfully and immediately modified to correspond with what the Government officers may deem the interests of com merce." I beg leave to suggest that the United States district attorney be instructed from the Department of Justice to withdraw the injunction issued at the instance of the Secretary of War, restraining the Illinois Central Railroad Company from proceeding with the construction of docks in the outer harbor of Chicago, upon the condition that the said company shall agree, in such form as the district attorney may consider best, to conform to the approved plans and limiting harbor-lines of the War Department in the construction of said docks. Very respectfully, your obedient servant, A. A. HUMPHREYS, Brigadier-General and Chief of Engineers. Hon. W. W. BELKNAP, A 23. UNITED STATES ENGINEER OFFICE, GENERAL: I have the honor to submit, for your approval, a modified cross-section for the breakwater at this harbor. I inclose a report by Assistant W. H. Hearding, on the subject of stone foundations for crib-piers, which fully sets forth the reasons which have led me to propose this modification. In the cross-section given, the depth of water is taken at 22 feet, 6 inches more than the average. The ultimate plan I propose is a stone breakwater, composed below the water-level of loose stone, and above of masonry. The first superstructure should be of crib-work, as now built, filled with loose stone. By the time this crib-work is decayed the foundation will have become permanent, and the work can be leveled off preparatory to putting on the permanent superstructure. The cross-section which I have given shows the maximum amount of stone required for the foundation, equal for a length of 50 feet of breakwater to 4363 cords, which would give for the cost, at $6 per cord, the price now paid for crib-filling, $2,619. The cost of a crib 50 feet long by 30 feet wide and 18 feet high is $3,140.39, to which amount should be added the varying expense of putting on the superstructure, due to the unequal settlement, tilting, and shifting of cribs. It is probable that the stone can be procured for $5 or $5.50 per cord for the foundation, as there will be less delay and handling than in filling cribs. At least 100 cords more than the amount given above could be added to each 50 feet of the breakwater without increasing the present cost of the work. The immediate benefit of the work will be greater than if the present plan is carried out, and at a less cost. The dotted lines show the cross-section to be given to the work when the stone is first thrown in. This will give protection to vessels lying in the "basin." The effect of the waves will be to flatten out the slope on the seaward side, and to carry the stones on the crest over to the inner slope. Stone will then be added until the foundation has become sufficiently permanent for the crib-superstructure. It is proposed to make the cribs for this part of the work 18 feet wide and 200 feet long. The stone will be leveled off so as to be 4 feet below the water-level before placing the cribs. The first cost of the work, with the cross-section shown by the dotted lines, will be $40 per running foot. The cost per running foot of the breakwater complete, according to the section, is $75. The cost per running foot of the breakwater, as now built, under the supposition that the cribs do not move from the position given them, for the same depth of water, is $103. This saving is due to the diminished width of the superstructure, and to the cheapness of stone in this locality. The cross-section of the foundation can, therefore, be very much increased without increasing the cost of the work, and a much more durable and satisfactory result will be obtained. Very respectfully, your obedient servant, Brigadier-General A. A. HUMPHREYS, D. C. HOUSTON, STONE FOUNDATIONS FOR CRIB-PIERS. Of the materials which are used in the construction of works for the improvement of harbors, stone is the principal constituent; first, by reason of the facility with which it can be obtained; and secondly, on account of its being the cheapest material, whose solidity and specific gravity are adequate to resist the force impelled by waves, or through the collisions to which it is constantly subjected at all points where commerce is conducted by means of steamers and sailing-vessels, and for the particular benefit of which the improvements at the mouths of rivers, by the construction of protection-piers, are usually made. The magnitude of such works is generally so extensive that, however cheaply this material can be procured, its economical use is carefully studied, and in order to effect a work of this character with as small an outlay as is practically consistent with the nature of the proposed improvement, as well as to adjust such artificial works in consonance with the physical character of the site to be improved, the material is placed in large boxes, or "cribs," as they are termed, which are framed of timber for this purpose, and by means of these are kept in a compact, symmetrical form. If it were not necessary to practice an economical use of means in the conduct of the various kinds of artificial aids to nature, material changes would undoubtedly be made in the methods adopted for their construction, as, in the case of pier-work, there is no doubt as to the superiority of cut-stone masonry over the use of rough fragmentary stone, incased in timber for such purpose; it is, therefore, the difference in the cost of the methods which partially determines the one to be adopted. The writer of this article is, however, of the opinion that stone, either natural or artificial, well bonded with cement, is the only proper material to use for piers in themselves, built apon proper foundations; but where an immediate improvement is urgent, and a strictly economical use of the means, which are available for such purpose, is necessary to be observed, as before stated, the reasons for incasing the stone in cribs for protection-piers to channels are obvious to any engineer of experience; for, as is well understood, at the outlets of rivers it is desirable to confine the river-current within the limits of as narrow a channel as is consistent with the requirements of navigation, in order that the scouring effect of the river-current may be maintained beyond the extremities of the piers to free the channel from sedimentary deposit. If the piers should be constructed of rough-quarried stone thrown in loosely on either side of the channel, the natural slope which the stone would assume thus deposited in water of sufficient depth for the purpose of navigation, might be a serious obstruction to the channel, and if the width between the piers should be increased to meet this difficulty, the scouring effect of the river-current would be diminished, while the volume of wave admitted during the prevalence of storms would be increased. The prejudicial effect from this latter cause is particularly marked where piers are constructed in continuation of the alignment of the outer reach of a river, which often forms an important portion of a harbor. Also, if the piers upon an exposed coast should be thus formed of stone of small size, they would be carried into the channel by the force of the seas, and form an obstruction; or if the adjacent beach should be of sand, and the piers formed by throwing in blocks of stone of a size sufficient to resist the force of the waves, the extraneous sand swept from the shores by littoral currents would be admitted into the channel through the interstices between the blocks and thus form an obstruction. In order, therefore, to effect an improvement of this character to meet the requirements at a medium cost, the system of incasing loose stone ballast in timber cribs has been adopted in constructing piers built to withstand the force of heavy seas, and in localities where they are not subjected to collisions by vessels, the strength of such cribs properly framed and bolted is adequate to the duty required in fresh-water seas. The cribs which are used by the officers of the United States Engineer Department for the improvement of lake-harbors are built with tight sides and ends, the timbers being 12 inches square, carefully framed and firmly bolted together, with an open gril lage-work for the bottom, the apertures between the timbers forming this grillage being large enough to admit of the free passage of the stone ballast. Opportunity is taken in fair weather to tow the cribs to the positions they are to occupy in the piers, and secure them in their respective places. When a crib has been thus conducted to its position and secured, a flooring of stout plank is laid over the upper center cross-ties, and a sufficiency of ballast is placed thereon to sink it to its bearings, after which it is filled as rapidly as possible. Care is taken to throw in stone of small size for the filling of the first or lower portion of the crib, which can run through the grillage. If the bed is soft, or of a loose character, quite a large percentage will be forced through the grillage by the superincumbent weight of stone. The upper portion of the crib is filled with stone of the largest size. On a moderately firm bed the artificial assistance thus rendered has been found sufficient to sustain the cribs in their proper positions, but where the natural bed is composed of loose, shifting sand, further assistance has been found necessary to prevent them from tilting, through the effect of the action of the sea upon the lake-bed. This detrimental effect first led to a discussion of the subject. It may be thought at the outset that, so long as the cribs forming a pier are not moved bodily, and do not actually dip so seriously as to endanger their tilting over, the utility of the pier is not impaired, upon the supposition that cribs thus tilted present the same impediment to the admittance of extraneous sand by preventing its percolation into the channel, just as they would if they remained in a proper vertical position. But if this result is not to be anticipated, there are good and sufficient reasons for using every effort to prevent their derangement. There is always more or less subsidence to cribs which are set upon shifting foundations, and, for this reason, it has been customary to construct the cribs with the side timbers projecting beyond the ends of a crib proper. The projections or horns have been usually extended 2 feet beyond the end timbers. The intervals between the cribs inclosed by the projecting timbers have been, therefore, 4 feet in width when the extensions have been in perfect conjunction, but through the subsidence of the cribs imperfect junctures are often produced, which increase the width of the intervals, leav ing an open space through which sediment in suspension can be introduced to the channel. Fascines of brush, or slabs, are tightly packed in the intervals and ballasted with stone to prevent the introduction of extraneous matter. The horns or projections are, however, a source of weakness, as they are easily fractured by collision, and for this reason other means should be adopted, which would be equally effective, for the purpose required, without impairing the strength of the general structure. But, to return to the subject of disarrangements or displacements: It being conceded that the stability and efficiency of piers depend upon the foundations upon which the cribs are set, this discussion hinges upon the best and cheapest method to be adopted for securing proper artificial foundations for cribs in loose soils. In localities where the sand is of great depth, piles should be driven until the clay or rock bed is reached, and the spaces between them filled with stone of small size; but the cost of this method is so great as to have heretofore excluded its practice in ordinary works of the character described. Where the overlying sand is but a few feet in thickness, it should be removed until the clay or rock bed is laid bare for the reception of the cribs. If a trench is dredged to a depth of 3 or 4 feet below the natural level of the lake-bed for their reception, the tilting will be diminished. If a dredging-machine cannot conveniently be obtained for the purpose, the next best method, (perhaps the best under any circumstances,) is to form a foundation of round bowlderstone of medium size, to a depth of 3 or 4 feet, upon the pier-alignment, to the full width of the pier, the surface of which should be made as level as practicable. Flat quarried stones should not be used for this purpose, as they are usually of a lighter character than bowlders, and are more easily removed by the water, when agitated; besides which they will not conform to as perfect a level by the pressure of the cribs. Bowlders are also preferable to quarried stone for crib-ballast. The action of the waves and the currents, induced by storms and other causes, cuts the sand from beneath the cribs and effects their subsidence, and during the process of constructing a work of this kind, the undermining effect will be particularly noticeable at the extremities of piers as each crib is set and subjected to the action of these forces. From these facts it is inferred that a combination of methods should be adopted, namely, by using loose stone for a foundation and confining the upper portion of the stone in well-framed cribs. As a preventive to the cutting out of sand at the base of the cribs, a distribution of stone along their sides has been effectively practiced; they have been usually thrown into a height of 3 or 4 feet, forming an apron to receive the shock of the waves, which are deflected downward upon their concussion with the vertical sides of the cribs; the cushion or apron thus formed prevents the water from washing out the sand at the angle formed by the crib and the lake-bed. As the stone used in the formation of the foundation would necessarily extend outside of the cribs, the additional quantity required to form the apron would not be as |