suspension of operations in June, 1870, was, that it was still necessary to remove 873 cubic yards, in order to reduce the bottom to the level of 25 feet below mean low water. In the latter part of July, 1870, operations were resumed at Hallett's Point, and directed to sinking further the bottom of the shaft, and to the commencement of the tunnels leading outward from the shaft. The tunnels radiate from a central position, and as the piers between these enlarged, intermediate tunnels are struck out, cross galleries, about 25 feet between their axes, are pierced through the piers separating the tunnels. The result of the operations of the fiscal year has been, the reduction of the floor of the shaft to the depth of 33 feet below mean low water, and the opening of tunnels and galleries to the following lengths: The cross dimensions of the tunnel vary as their penetration increases, the height becoming less. The dimensions written below correspond, the first in order, to the commencement, and the second, to the present end of the tunnels. Tunnel No. 1, 22 feet high by 9 feet wide; 14 feet high by 13 feet wide. Tunnel No. 2, 214 feet high by 10 feet wide; 11 feet high by 12 feet wide. Tunnel No. 3, 21 feet high by 11 feet wide; 14 feet high by 11 feet wide. Tunnel No. 4, 22 feet high by 103 feet wide; 8.7 feet high by 113 feet wide. Tunnel No. 5, 20 feet high by 11 feet wide; 7 feet high by 12 feet wide. Tunnel No. 6, 19 feet high by 9 feet wide; 113 feet high by 103 feet wide. Tunnel No. 7, 19 feet high by 11 feet wide; 12 feet high by 12 feet wide. Tunnel No. 8, 193 feet high by 9.7 feet wide: 13 feet high by 9 feet wide. Tunnel No. 9, 17 feet high by 12.7 feet wide; 8 feet high by 9 feet wide. Tunnel No. 10, 12 feet high by 10 feet wide; 8 feet high by 14 feet wide. Gallery No. 1, 12 feet high by 9 feet wide. Gallery No. 2, 103 feet high by 10 feet wide. The amount of rock excavated and removed from the shaft and tunnels during the fiscal year was 8,306 cubic yards. The roof over the tunnel and galleries is about 10 feet in thickness. The rock is a gneiss, with a stratification nearly vertical; it is generally hard to the drill, and requires great care in blasting, to avoid spreading the seams, and opening copious leaks. All of the tunnels and galleries have hitherto have been driven by hand-drilling. The machinery for drilling by steam or compressed air has been ordered, and is expected soon to be in place. The nature of the rock, the little adhesion between the strata, the narrow margin between the workmen and the water above, have necessitated the use of shallow holes and of small charges of gunpowder or nitro-glycerine. The progress has necessarily been slow, since no advan tage could be taken of deep holes and large charges, to which tunuels on land pierced through large masses of rock have been indebted for their comparatively rapid rate. From the experience in hand-drilling, it is estimated that the progress at Hallett's Point cannot exceed one-tenth of that which could be attained on land in tunnels similar in all other respects and driven by machinedrills. The use of steam or air drills will expedite matters, perhaps double the rate, and it is indispensable to try their effect, but the necessity of shallow holes and small charges will much detract from the progress which has been attained by their use when left unhampered by such restrictions as are set forth above. The ruling idea in conducting the work has been to take out all the rock which a due regard for strength in the remaining parts would tolerate, and in this view the tunnels have been made high and wide. So far the leakage has drained into the shaft, from which it has been lifted by one pump of ordinary power. It will shortly become necessary, in order to preserve the necessary thickness of ten feet of roofing, to sink the floor of the tunnels. At the present time it is deemed advisable, instead of sinking the whole level, including the shaft, to depress the floor of each tunnel, inclining outward sufficiently to obtain in each case the necessary depth. Another pump, to drain the working faces of the tunnels, will be employed. The leakage, as to quantity, has never yet troubled the work. One pump, not worked to its full capacity, has hitherto sufficed, and in this respect there seems to be no cause of apprehension. After the tunnels are driven to their full extent, and the galleries excavated, the question will arise whether to blow up the rock as it stands, or, taking away the piers, to sink the level of the excavation sufficient to receive the debris of the roof. Fortunately it is not imperative to decide the question at present, and in the interval further study of the matter, as to relative certainty, cost, and rapidity of execution will precisely determine which of the methods would be preferable. At an early date, with the view of applying machinery to expedite the work of drilling at Hallett's Point, public advertisements inviting proposals for drilling were inserted in the daily papers. The abstract of bids is inclosed herewith. The hids not being deemed advantageous to the public interests, were, with the consent of the Chief of Engineers, rejected. Subsequently arrangements were made to have 20,000 lineal feet of rock-drilling executed at 83 cents per foot, the United States supplying the power. A diamond tunnel-drill has also been purchased, this form of drill, after a trial in the tunnels, having promised good results; but, in addition, the ability to "prospect" ahead of our work, which is a specialty of the diamond drill, may prove of incalculable advantage. STEAM-DRILLING SCOW. This machine was first put to work in the winter of 1870–71; two rounds of charges were exploded in Diamond Reef. The appearance of floating ice compelled a suspension of work, which was resumed in the spring upon the same reef, and continued until the solid bed-rock had been covered by the blasts, of which six additional rounds were fired on this reef. Pending the removal of the broken rock, the drilling-scow was moved to Coenties Reef, and four rounds of holes were blasted. As the grapple-boats were not employed until the termination of the fiscal year, there is no report of rock removed from these reefs embodied in this paper. The grapple-boats are hired by the day. Experience derived from our work has shown the necessity of large charges, which vary, according to the depth of the hole, from 30 to 55 pounds of nitro-glycerine for each. The holes vary in depth from 7 to 13 feet; at top, 44 inches; and at bottom, a little over 3 inches in diameter. Eight of these holes are placed at equal distances on the circumference of a circle 20 feet in diameter, and one in the center of the circle. During the months of May and June the drilling-boat encountered six collisions, several of which did much damage by forcing the scow upon the dome. The drill-pipes above the dome were carried off, the drills in the holes broken, and the telescope of the dome crushed in so as to be incapable of being worked. The delays and loss of time due to these collisions have likewise been great. The scow has not been at all damaged by the collisions. The drills are lifted by steam-power and allowed to drop by their weight. The drills often unscrew, and sometimes break in the holes; and when an open seam is encountered, the drill has a tendency "to run;" i. e., follow the seam and become bound. These mishaps cause much delay and loss of time, and unless the portion of the drill left in the hole can be extracted, the loss likewise of the hole for blasting purposes. These difficulties led early to a consideration of the propriety of placing improved drilling-machines upon the dome, and in this way work the drills directly, and with vastly quicker results; but it was anticipated, as has actually happened, that a collision, by forcing the scow upon the dome, would sweep off anything attached to its surface, and hence such project was never carried out. Recent investigations on the subject have, however, led to the opinion that, by placing the machine on the scow, it was not impracticable, with a suitable connection by flexible joints, to work the drills which are set in the tubes, and experiments to this end will be undertaken during the coming winter. It has been found perfectly practicable to hold the boat in a position fixed, or at least imperceptibly varied, during the prevalence of the strongest currents in the lower part of the East River. Work will be continued upon Coenties Reef and Diamond Reef during the present season, and the grapple-boats set to work to remove the broken stone after the blast. The steam-drilling scow has fully proved its ability to perform good practical work. Respectfully submitted. JOHN NEWTON, Lieutenant Colonel Engineers, Brevet Major General. Brevet Major General A. A. HUMPHREYS, Chief of Engineers, Washington, D. C. Abstract of bids for drilling by machinery at Hallett's Point, New York; opened January 11, James Russell per For all holes not exceeding 2 inches in diameter and 3 feet in depth, 82 25 lineal foot; for all holes of same diameter and over 3 feet deep, 82 35 per lineal foot, aircompressors to be furnished by contractor. For drilling the above holes, the air-compressors to be furnished by the Government, the price will be: for holes 3 feet in depth, $1 30 per linear foot; for holes over 3 feet in depth, $1 40 per linear foot. Severance & Holt.. For holes from 14 to 2 inches in diameter and from 1 to 3 feet long, and in some cases 9 feet long, for the uniform price of $2 per linear foot; air-compressors to be furnished by the Government. JOHN NEWTON, Lieutenant Colonel Engineers and Brevet Major General. APPENDIX T. ENGINEER OFFICE, UNITED STATES ARMY, GENERAL: I have the honor to submit the annual report upon the works of survey and improvement specially under my direction during the fiscal year ending June 30, 1871, together with an outline of operations from June 30 to present date, viz: Improvement of Providence River, Rhode Island. Removal of Bulk-head Rock, Providence River, Rhode Island. Construction of breakwater at Block Island, Rhode Island. Survey and improvement of Pawcatuck River, Rhode Island and Connecticut. Survey of Stonington Harbor, Connecticut. Improvement of Thames River, Connecticut. Improvement of Connecticut River above Hartford, and below Holyoke. Improvement of New Haven Harbor. Survey and improvement of the Housatonic River below Derby, Connecticut. Survey and improvement of Bridgeport Harbor, Connecticut. Survey of Southport Harbor, Connecticut. Improvement of Westport Harbor, Connecticut. Survey of Norwalk Harbor, Connecticut. Survey of Huntington Harbor, Long Island, New York. Survey and improvement of Port Jefferson Harbor, Long Island, New York. Survey and improvement of Peconic River, Long Island, New York. All of which are respectfully submitted. Brigadier General A. A. HUMPHREYS, G. K. WARREN, Major of Engineers, &c. Chief of Engineers, U. S. Army, Washington, D. C. T 1. IMPROVEMENT OF PROVIDENCE RIVER, RHODE ISLAND. The work under the appropriation of $5,000, made by the act approved July 11, 1870, was in progress at the date of my last annual report, September 30, 1870, (see p. 449 of printed annual report of the Chief of Engineers for 1870,) under a contract for dredging, duly made with Mr. Thomas J. Hill, of Providence, at the rate of 25 cents per cubic yard. Mr. Hill completed the removal of 18,200.5 cubic yards of material in October. This amount included the extraction of sixty-seven piles whose tops had been formerly broken off and left to remain, giving a depth on them of only 12 feet at mean low water in the main channel. There was at the Crook, (which is in the Providence Channel, just above the junction with the Seekonk Channel,) on the completion of this contract, practically a channel-way up to Fox Point wharf, with minimum widths as follows: For 130 feet width, 14 feet depth at mean low water. It is believed there is very little tendency for this excavated channel at the Crook to fill up, and any further appropriation would be required only to widen the passage-way on the west side. The widening at this point tends also to straighten the channel-way, and would improve the entrance for coasters, and give anchorage without obstructing the passage-way. I send with this report a map showing the condition of the channelway at the Crook, as left by the operations conducted under my direction in 1870. I had an examination and sketch-map made when I commenced operations, but circumstances prevented a correct determination at the time of the plane of mean low water, and this preliminary work could not afterward be accurately connected with the subsequent survey. As far as I know, Colonel Houston did not cause any surveys to be made while the dredging operations were conducted under him, and there is no map showing the condition of the channel on the completion of the dredging done at the Crook in 1867. The determination of the plane of mean low water by direct observation was a necessity, for we were unable to find the bench marks of the United States Coast Survey, or any other survey. There is too little attention paid to establishing proper "bench marks," and I cannot, in all cases, secure proper compliance with my views of their importance, even from my own assistants. No public work should be done without leaving behind a perfect record of it, in every respect, if possible. I append to my report the report of Mr. N. E. Russell, who superintended the work of dredging last year, and made a map of the locality after the work closed. The method he employed in determining mean low and mean high water-levels is only satisfactory when the observations cover a whole lunation, but his determination practically agrees with the United States Coast Survey's determination of the rise and fall of the tide. The future continuation of a work like this at the Crook, in the Providence River, is a question more of facilitating navigation than of removing an obstruction to it; and to aid in its consideration I present the following history of what has been done at this point heretofore. The first work done by the United States engineers in the Providence River was a survey, in March 1853, by Lieutenant Rosencrans, United States Engineers, authorized by an appropriation of $1,500, made for this purpose in August, 1852. At the same time an appropriation of $5,000 was made for improvement. The improvement was carried on under Captain George Dutton, United States Engineers, in the season of 1853, (and his reports will be found in the documents accompanying the President's message at the meeting of Congress in 1853.) In his report of April 20, 1853, he attributes the formation of the shoal at the Crook to "the great predominance of the current of the Seekonk River, crossing that of the Providence River." In his report dated October 20, 1853, he says: The lump or obstruction known as the Crook, and composed of stiff mud and shells, upon which there was originally, according to the survey, only 4.3 feet water at low tide, has been removed to the depth of from 9 to 10 feet (and the channel generally irregularly to 9 feet, at low water, throughout its whole extent) at the present date, (with a slight exception, which it is expected to accomplish, and some widening to the westward at the lower mouth, with the present means.) |