UNITED STATES ENGINEER OFFICE, Keokuk, October 24, 1870. GENERAL: In accordance with your orders, I have the honor to make the following report on the improvement of the Des Moines Rapids of the Mississippi River, including the work already done, its present state, and the estimated quantities of work necessary to place it in the hands of the public for use, all being brought to the 30th of September, 1870.

The work, as determined in the fall of 1867, by a board consisting, besides yourself, of Colonel J. N. Macomb, Brevet Major General G. K. Warren, Colonel W. Milnor Roberts, and Captain P. C. Hains, the latter acting as recorder, was as follows:

1st. The excavation of a channel extending from the northern end of the island, at Montrose, to Nashville, a distance of two and a half iniles. This excavation not to be continuous, but to be made through the "chains" or patches that might separate the portions of deep water, together with the formation of a bay or entrance harbor, with deep water, at the head of the guard-lock.

2d. A canal from Nashville, at the head of the rapids, to Keokuk, at their foot, with the necessary locks and embankment.

The work necessary for the canal is hence divided into two distinct parts-the canal proper or "section-work," and the three locks necessary for the fall of 19.75 feet from Nashville to Keokuk; and I will consider the matter under the two heads given, leaving out entirely the Montrose Channel, on which no work has yet been done.

On the canal the following is the amount of work done: On earth excavation, 546,596 cubic yards, which leaves to be excavated, according to the original estimate, 119,993 cubic yards; but as there have been 27,421 yards excavated in excess of the original estimate at dif ferent points on the line, there really remains 147,414 cubic yards of earth to be excavated.

This large discrepancy arises from orders given during the progress of the work, on account of contingencies that could not be foreseen, and not from any prime errors in the first calculations; the principal cause being an order to carry the excavation of the silt and mud of the river bottom, where it occurred, to the rock bottom-a necessary thing, but not considered in the first estimate.

ON ROCK EXCAVATION.

There have been 248,908 cubic yards excavated, leaving, according to the original estimate, 29,086 yards to complete the work, a quantity which is nearly or quite correct. Hence on excavation of earth we have 77 per cent. done, and of stone, 89 per cent. Although this comprehends the bulk of excavation of the prism of the canal, there yet remains quite an amount of work to be done in clearing up the bottom of the canal and bringing every point down to the accepted grade.

On the embankment, which has necessarily followed the excavation of the prism, the work stands as follows, the materials having been entirely supplied from the excavation :

From the head of the guard-lock, station 32, it stands at grade down to station 84, a distance of 5,200 feet; thence 5,200 feet, to station 136, it is 2 feet below grade; thence 4,200 feet, to station 178, it is 4 feet below grade; thence to station 346, or 16,800 feet, it is up to grade; then for 3,000 feet, to station 376, it is 3 feet below grade; and thence gradu

ally descending through a distance of 3,800 feet to station 414, it runs out to nothing, or 14 feet below grade.

The riprap base-wall, or "toe" of the embankment, is completed from here to the head of the lower lock, at station 424, or 1000 feet, and it is 14 feet below grade.

The embankment slope is to be covered with a wall of dry stone outside, at a slope of 1 on 13 and of 1 on 14 on the inside, while the top is to be covered to a depth of 10 inches with broken stone of the usual size for "macadamizing."

The walls and top-dressing are finished from the head of the guardlock to station 75, a distance of 4,300 feet; thence the top wall extends in an unfinished condition, from 5 feet to 6 feet below grade, to station 81, and stops.

The inside wall extends in a similar condition to station 79, 400 feet, and then stops.

It then recommences at station 94, runs about 7 feet below grade to station 98, or 400 feet, and then stops.

The next piece of outside wall begins at station 138, and continues 4 feet below grade, to station 157, a distance of 1,900 feet; thence it continues gradually decreasing to nothing at station 162, or 500 feet farther. It begins again at station 180 and continues, entirely finished to grade, to station 236, a distance of 5,600 feet; thence at an average elevation of 7 feet below grade, it extends to station 262, a distance of 2,600 feet, where it stops.

The inside wall is finished up to grade for 400 feet from station 223 to station 227.

Below Price's Creek the outside wall again commences at station 295, and continues at an average of 3 feet below grade to station 345, a distance of 5,000 feet, where it ends, to recommence at station 352, and extends 700 feet to station 359, at an elevation of 6 feet below grade. Here the outside wall finally ends, further work being dependent on the progress and settlement of the embankment.

The inside wall of the embankment begins again at station 314, and runs 2 feet below grade to station 324, a distance of 1,000 feet. Here this wall finally ends. The original estimate of wall, both inside and out, was 75,000 cubic yards; of this 13,915 have been built, leaving to complete the work 61,085 cubic yards.

The original estimate required the changing of the track of the C. B. and Q. R. R. for one and one-half miles, and the raising of the grade at Price's Creek for three-fourths of a mile. This has been done satisfactorily to the railroad company. The last estimate of this work was made and paid in September, 1870.

SECOND LOCK WORK.

In the original plan of the lower lock, it was proposed to make the pier at the lower end 300 feet in length, but on account of its great expense, and the comparatively small benefits to be obtained from this great extension, the length of this pier has been reduced to 150 feet. No other plans have been materially changed. The lock is thus 350 feet in length and 80 feet wide, filled and emptied by culverts running behind the main walls and connecting with the lock-chamber by small branches.

The work was originally let on August 15, 1868, to Ephraim Owen, to cover the sum of $220,000. He commenced work immediately and

has pursued it up to date, except when stopped by high water, with the following results:

1. Earth excavation completed.-Amount excavated, 10,414 cubic yards. 2. Earth embankment.-The shore embankment is finished up to grade throughout, and is covered with macadam to an average depth of ten inches. The river embankment averages 4 feet 6 inches below grade. Total amount of embankment, 83,447.73 cubic yards.

3. Rock excavation.-The rock in the lock-prison has been entirely excavated. Work is still in progress at the lower bay, and will be finished in October. Total amount of rock excavated, 14,310.57 cubic yards.

4. Concrete masonry.-The entire foundations for the lock-walls have been made in concrete from 6 inches to 18 inches thick. Great care has been taken in this work, both in the preparation and laying. The proportions used are as follows: 1 part cement, 14 parts sand, and 3 parts of broken stone. Total amount of concrete laid, 1,051.57 cubic yards.

5. Lining. This designation has been given to the stone laid between the lock-wall and the embankment, and to the covering of the shore embankment. No accurate estimate can be made of what will be required to complete the work. Total amount of lining in work, 1,698 cubic yards.

6. Puddling.-Puddling has been used freely whenever the state of the embankment at any point has demanded it. Total amount of puddling, 991.10 cubic yards.

7. Lead and antimony.-This item called for in the contract has been furnished to the amount of 410 pounds, used in cementing the iron-work connected with the anchoring and suspension rods.

8. Wrought iron.-Four thousand two hundred and thirty-two pounds of wrought iron have been prepared and placed in position as anchoring-rods for the gates. The iron used is Tennessee "AI;" tensile strength, 72,000 pounds; 12 inch square, or 2 inches round.

9. Timber. The only timber used has been in the foundation of the river-side vertical wall. Amount, 760 feet, board measure.

10. Masonry.-2,433.21 cubic yards constructing cut-stone masonry; 1,381.39 cubic yards constructing cut-stone masonry completing; 3,721.97 cubic yards constructing cut-stone masonry partly done. The latter item is for dressing the stone, for which a relative price of $5 is estimated out of the contract price of $7. The second refers to the setting of the dressed stone.

The following is the state of the masonry: The pier-head is finished. to within four courses of the top at the lower end; the portion nearest the wing and the wing itself, on lower left side, is completed, and the coping in position. The main lock-wall is completed, and in condition to receive the coping as far as the upper end of the lower gate recess; from this point up stream, the main lock-wall is raised five courses for a distance of 180 feet, and also the back wall of the supply-culvert to the skew-back.

On the shore side of the lock three courses are laid, from the lower wing-wall to the first culvert in the gate recess. The lower mitre-sill is completed and ready to receive the coping.

11. Lumber for gates.-A contract was made in 1869, with James Reardon, to furnish, delivered at the planing-mills in Keokuk, the necessary lumber for the gates of the three locks for $45 per M., board measure, for the best white oak of specific dimensions. After furnishing 42,680 feet, Mr. Reardon declared his inability to fulfil his contract, and a new one was given to Mr. James Carroll for $65 per M.

Mr. Carroll filled the contract in August, 1870, having furnished 125,180 feet, board measure. The quality of this lumber is of the best, and has been furnished of the dimensions given at this office.

12. Planing. The planing was let to Messrs. Copeland, Gray & McClelland at $20 per M., to be delivered on the cars at their mill. On September 30 they had planed 116,644 feet. On these heavy hewn timbers their cutting has been less than half as much more than on thin boards or planks.

13. Iron. The necessary iron for the locks, gates, &c., was let to Morris Sellers, at 5 cents per pound. The cast iron furnished by him has a tensile strength of 21,500 pounds per square inch. He has furnished, up to September 30, 98,496 pounds cast iron in the shape of hollow quoins, wickets, heel-plates, &c.

14. Cement. The cement in use has been furnished by James Clark & Son, of Utica, Illinois. It is a slow-setting, light-colored cement, but for that reason is superior for our purposes to any other that can be obtained here. Their final estimate, dated September 30, was for 3,353 casks, at $2 60 per cask.

It is proposed hereafter to obtain the cement in bags, thereby saving the cost of the barrel, say 25 cents for every 300 pounds.

Very respectfully, your obedient servant,

A. H. BURNHAM,

Captain Engineers and Brevet Major, U. S. A., in local charge.

Brevet Major General J. H. WILSON,

Lieutenant Colonel, U. S. Army, Keokuk, Iowa.

UNITED STATES ENGINEER OFFICE,

Rock Island, Illinois, October 7, 1870.

GENERAL: I have the honor to report the following operations for the improvement of the Rock Island Rapids, for the quarter ending September 30, 1870.

The work on the obstructions has been confined to breaking up detached patches of rock with the chisel, and removing with the dredge the broken rock, together with loose rock left in the channel the year previous, and certain portions of the coffer-dams and cribs protecting them.

The dredge worked upon Campbell's Chain, removing portions of the head and foot of the coffer-dam until the 14th of July, when it was taken up to Sycamore Chain, to remove enough of the lower dam to admit of the passage of steamers through the channel. After it had completed this work it was taken to the head of Sycamore Chain, to remove all the cribs and portions of coffer-dam left in the channel. Meanwhile, the chisel-boat was placed on the ridge of rock covered by the head of the small dam at Sycamore Chain, and the work of breaking up the rock commenced. The dredge, meanwhile, continued clearing up the débris at the head of the chain until the 27th, when the channel was reported clear at this point. The dredge then returned to the foot of the chain, and cleared away more of the coffer-dam from the channel. It was then taken down to the head of Campbell's Chain, to remove broken rock left in the channel the preceding season. It remained here until the 24th of August, when it was shifted, to make room for the steamer and attached sounding-boats.

The dredge dropped down to a position about 1,000 feet below the

foot of Campbell's Chain dam, and removed a quantity of broken rock and boulders from the channel. After this, it returned to its former position at the head of the chain, removing all the loose rock that could be found, giving a very good channel through the chain.

The chisel had been at work steadily, breaking up rock at the head of the Little Sycamore dam, until the 7th of September, when it was taken to the foot of the dam to break up a detached piece of rock.

The dredge took its place on the ridge, remaining here until the 14th, when the high stage of the water forced it off. The contractors dropped it down and commenced removing the foot of the coffer-dam, which I stopped, thinking it better to leave it in, for the time, as they had always, before that time, desired the foot to be left in, saying that it aided their work, and I did not see any good reason for taking it up then.

The opportunity was taken of high water to take the chisel boat to Le Claire and repair the hull. On the 22d the boat was brought down from Le Claire and placed, again on the chain. By the close of the month all the broken rock was reported as cleared up, and the foot of the coffer-dam removed. Examination showed that a great deal of very finely pulverized rock had been deposited by the current over the bottom within the small dam. I have no doubt that now that the foot of the dam has been taken out, all this will be swept away; and I purpose to make another examination of this before my connection with the work terminates.

Very high water was experienced during part of September, which, together with rain and wind, interfered greatly with field-work.

During July the line of levels on, the Iowa side of the river, taken in 1867, was tested, but the results were not perfectly satisfactory, and I had to leave this question until the completion of the soundings over the different chains, for which I was then preparing. I also ran, myself, over portions of the line on the Illinois side of the river. My desire was to have each side tested by a different person, and to have a third party run the entire circuit-about thirty miles in all-calling each side of the river fifteen miles in length. I will add that a party is now out, October 7th, engaged in leveling the circuit.

The steamer Iowa City was chartered, on the 13th of August, for the purpose of sounding the rapids with attached skiffs or flats. The party was organized in the usual manner, and in charge of Major Hoffman, and worked steadily, excepting when interrupted by rain and wind, until the 6th of September, making and recording the following soundings: On the Lower Chain ...

On Duck Creek...

On Moline

On Campbell's..

On Sycamore.

On Smith's.

In all.....

5,000 soundings. 19, 000 soundings. 11, 000 soundings. 21, 000 soundings. 13, 000 soundings. 7,400 soundings.

76, 400 soundings.

The soundings on the Lower Chain and Smith's Chain were necessary, in order to give more information about the bottom of the river, the soundings taken in 1867 being too meagre. The soundings on the other chains were mainly taken to verify work.

The party returned to the office, and the assistants were set at work to reduce and plot the more important of the soundings for immediate