cubic feet. These experiments were not carried to the extent of raising the head of the out-flow to the under side of the limestone for fear of the water forcing a passage around the lower end of the lining, which only extended some 25 feet below the spring. It is hoped that the amount raised by the citizens, together with the small sum unexpended of the last appropriation, may suffice to finish the plugging of the east branch, the extending of the lining below the spring some 40 feet, and the putting in of two timber bulk-heads in the lower branches of the tunnel below the spring. A portion of the toe of the apron at the west side was broken down by the ice resting upon it, which cannot be repaired until low water. The openings through the upper portion of the limestone ledge (marked E) will also be plugged with well-rammed gravel. III-PLANS AND RECOMMENDATIONS OF THE BOARD FOR THE PRESERVATION OF THE FALLS. In considering the plans for the preservation of the Falls of Saint Anthony it may be well to recapitulate the existing dangers: 1st. There is the danger of the destruction of the limestone covering at the falls by reason of the upper layers being disintegrated and separated by the action of frost, and carried away by the erosive action of heavy bodies of ice and logs passing over the falls. There is less immediate danger from this cause than from the following: 2d. The constant wearing away of the sandstone at the foot of the falls by the falling water, and the consequent falling down of the limestone, which process was very rapid previous to the building of the ex isting apron. 3d. The danger of the water passing from the head of the ledge through the sandstone, under the limestone covering, to the foot of the falls. The danger from this cause is at present the most threatening of all. In general terms, the first danger would be obviated by having a depth of at least 4 feet of water over all parts of the limestone; the second, by keeping in good repair and extending the existing apron; and the third, by a dike extending from a dry stratum of the sand-rock, below the soft strata up to the limestone ledge, and the wall recommended by the board of 1872. The board, therefore, presents the following plans and estimates for the execution of the works immediately necessary: 1st. Two dams should be constructed along the lines G and II, of timber cribs, well bolted to the rock and filled with stone, to have an upper slope of and a lower slope of 3, both slopes to be covered with 12inch squared timber. The foot of the lower dam to be connected with the apron, and the upper dam to have a toe 20 feet in width, and all salient angles to be covered with boiler plates. The lower dam should be 44 feet high, and the upper 4 feet high. A tracing showing crosssections of these dams is herewith appended. It is estimated that these dams will cost $24,420. 2d. The apron should be put in thorough repair, and extended down stream on the west side of Hennepin Island. The amount required for this work is estimated at $65,000. 34. From the description of the present condition of affairs and the history of what has taken place at the locality since the board of engineers met at Minneapolis in August, 1872, it is apparent that the dangers threatening the integrity of the Falls of Saint Anthony have considerably increased, and are of such a nature as to convince the pres ent board that the opinions then expressed were correct. The present board is satisfied that if the funds had been provided to carry into effect the recommendations then made, the remedial measures would have proven as complete as the nature of the case admitted, or as the board of 1872 expected. But the changed conditions, while they indicate the propriety of the former recommendations, render advisable some modification of the measures to be at once adopted, leaving to the future the carrying into effect of the principal features of the original plan. The development of the connection between "break No. 3" and the spring at the bifurcation of the tunnel and the fourth break" into the tunnel, indicate disturbances in the soft or bowlder stratum of unknown extent and location. The wall at the head of the limestone ledge, proposed by the board of 1872, would effectually cut off the percolations through the soft stratum beneath the limestone and prevent the dangers arising from such percolation, but its construction now would be attended with greater difliculty as well as greater risk, and the cost would be much greater than was formerly estimated. The board is now reluctantly constrained to recommend that measures more readily executed and involving less expenditure be undertaken and completed as soon as practicable, with the view of preventing additional injuries resulting to the falls, which may hasten their final destruction. These measures are the introduction of a dike of concrete to extend across the river at a position lower down the channel, along a line a short distance above the apron on the Minneapolis side, upon the tracé indicated on the drawing which accompanies this report. This dike should be constructed in a tunnel to be excavated on the proposed line, whose bottom should be in that homogeneous stratum which is some 38 feet below the limestone, extending up to the limestone, and at least 4 feet in width. This plan of a dike is only proposed because of the change of circumstances since the report of the board of engineers of 1872, rendering a more speedy relief necessary, and because it now seems to present less difficulties in its construction, and will serve to do away with a very great danger, existing by reason of the rapid disintegration of the sandrock near the head of the ledge. The board is of the opinion that the plan of the board of 1872 should ultimately be carried out, and the whole mass of the sandstone between the crest of the falls and the head of the ledge be preserved by inclosing it between the wall proposed by the board of 1872 and the dike now recommended to be constructed. The length of the dike would be abou 2,000 feet, and is estimated to cost as follows: Of the amount estimated the sum of $219,792 should be made imme diately available. Experience has clearly demonstrated the correctness of the recommendation of the board of 1872, that only a sum as large as this will enable any one to solve this problem. The smaller sums which have been appropriated for this work, both by Congress and individuals, since that time have been exclusively expended in repairing damages which occurred in consequence of the utter inability of those in charge to carry out the thorough plan for want of funds. The board cannot conclude without expressing its regret, that notwithstanding the recommendations of the board of 1872, with reference to obstructions placed in the bed of the river at this locality, none of them have been removed, but on the contrary new ones erected. It is strange that the interests dependent upon the preservation of the Falls of Saint Anthony should continue to employ means tending so strongly to its entire destruction, and the board must renew the condemnation expressed by the board of 1872 of this practice. All of which is respectfully submitted. Brig. Gen. A. A. HUMPHREYS, J. N. MACOMB, Lieut. Col. of Engineers. Major of Engineers. Major of Engineers. F. U. FARQUHAR, Major of Engineers, U. S. A. Chief of Engineers, U. S. A. Correspondence relative to money contributed by the citizens of Minneapolis, Minnesota. UNITED STATES ENGINEER OFFICE, GENERAL: I have the honor to inclose a copy of a letter just received from H. T. Welles, esq., who was president of one of the committees of citizens of Minneapolis under whose supervision the money contributed by the citizens for the preservation of the Falls of Saint Anthony was expended. By it will be seen that the amount reported by the board of engineers convened in Minneapolis during the last month, as contributed by the citizens and city of Minneapolis, was too small. The amount should be, as per inclosed letter $333,000. The amount reported by the board was taken from the report made by the citizens of Minneapolis to the board of 1872, (see page 304 Annual Report of the Chief of Engineers for 1872.) I have no doubt Mr. Welles' figures are correct, and that the report of the board of engineers for 1874 should be amended. Very respectfully, your obedient servant, Brig. Gen. A. A. HUMPHREYS, Chief of Engineers, U. S. A. F. U. FARQUHAR, |