This differs from the estimate submitted in my last annual report, as in that no estimate was made for Montrose Channel, and the quantities were taken from the original estimate. Changes in the character of the work, and especially in the prices bid, have also caused a difference, but it will be seen that the total amount varies but little from the original estimate, and is still within it.

For further information on the minutiae of the work, I have the honor to invite your attention to the report of Captain A. H. Burnham, in local charge since August 1, 1870.

IMPROVEMENT OF THE ROCK ISLAND RAPIDS.

During the quarter ending September 30, 1870, operations upon this improvement have been confined to the removal of isolated patches and débris by the chisel-boats, and the removal of the obstructions caused by coffer-dams, which were laid at the commencement of the work. The engineer party, besides testing levels on each shore, have made 80,400 soundings, for the purpose of verifying the work done; these soundings are now being plotted by Lieutenant E. F. Hoffman, under whose immediate directions they were made.

For particular information, I have the honor to refer you to the report of Captain Charles J. Allen, Corps of Engineers, herein inclosed.

In pursuance of authority of the Bureau of Engineers, I caused an advertisement to be inserted in the leading newspapers, soliciting proposals for the continuance of work upon this improvement, and although the letting was made after my relinquishment of the supervision of the work, it is not out of place for me to mention that the lowest bid was submitted by Elliott Harroun, at the rate of $14 per cubic yard at Smith's Chain, and at $8 per yard for all the rest of the work. At these rates it will require $225,000, including 10 per cent. added for contingencies to complete the improvement. This sum should be appropriated without delay.

IMPROVEMENT OF THE ILLINOIS RIVER.

The work on the Illinois River, during the time which has elapsed since my last annual report, has been the excavation of 48,391.6 cubic yards of earth, taken from the channel at the bars, which caused the greatest trouble to navigation.

To complete the work, it is estimated that $250,000 will be required; this amount depends on the date of completion of the work, as more will be demanded if this date is after the close of the season of 1872.

Annexed will be found the report of Civil Engineer Assistant Robert E. McMath, (under whose immediate charge this improvement has been,) to which I have the honor to invite your attention.

As in the case of the improvement of the Rock Island Rapids, I advertised for bids for the continuance of this work. The lowest offered was by Messrs. J. T. Hayden & Co., of Chicago, at the rate of 243 cents per cubic yard.

SURVEY FOR A SHIP CANAL ROUTE FROM HENNEPIN, ILLINOIS, TO ROCK ISLAND.

In accordance with directions received from your office, dated July 23, 1870, I proceeded immediately to organize, equip, and send into the field a party for this survey. This party was placed under the charge of Civil Engineer Assistant H. A. Ulfers, to whom I gave instructions, of which the following is a copy:

UNITED STATES ENGINEER OFFICE,
Keokuk, Iowa, September 5, 1870.

SIR: An allotment of $12,000 having been made for the survey of a "ship" canal route from the Illinois River, near Hennepin, to the Mississippi River, at or near Rock Island, Illinois, you are hereby placed in charge of that work.

You will commence the survey on the Illinois River, connecting with the river improvement works now in progress at Henry; ascend the valley of Bureau Creek, and examine thoroughly the water-shed between Bureau Creek and Green River, for a summit level. Connection will thence be made with the nearest available point on Rock River, to supply water to the summit. The explorations for this purpose will be made with a view to construct a navigable feeder. The descent to the Mississippi River will be effected by the valley of Green River. At Rock Island connection will be made with the surveys and levels of the Rock Island Rapids improvement. Careful gauges will be made of Bureau Creek, Green River, and Rock River, to determine the quantities of water available at the lowest stages.

The instrumental survey is to be connected, whenever practicable, with the corners of the general land survey.

Compass-bearings are to be recorded in connection with the angle-readings. The rear chainman will be furnished with a field-book, in which to record all distances, independently of the engineer in charge of the transit.

You will pay particular attention to the geological conformation of the country, and make note of all rock available for building purposes. All information as to depth of wells and character of the soil they are sunk into, will be valuable. Frequent cross-sections will be run across the valleys, sufficient to furnish contour-lines on the maps.

For the convenience of the leveling party, temporary stakes will be set every two hundred feet. Bench-marks will be established at least one in every mile; besides which, the elevations of water-tables, &c., of all permanent buildings along the route, will be entered in the level-books.

If time will allow, at the completion of the survey, you will turn back with the leveling party, and test all benches on the main route. All instruments, when not in use, will be kept boxed up and locked.

You will send to this office full weekly reports of progress, together with your postoffice address for the ensuing week.

All calculations and estimates for excavation, locks, &c., are to be based on the dimensions recommended for the enlarged Illinois and Michigan Canal.

You will be careful to limit your expenditures for this survey, and under no circumstances exceed the sum set apart for this purpose.

Very respectfully, your obedient servant,

H. A. ULFFERS,

J. H. WILSON,

Lieutenant Colonel and Brevet Major General, U. S. A.

Civil Engineer Assistant. Colonel Ulffers and party left this place for Henry, Illinois, on the 5th of September, and immediately proceeded with the survey. During the month of September they were much delayed by the heavy rains; they were, however, enabled to carry the work up the Illinois River, from Henry to Hennepin, and westward from Hennepin twenty-one miles. The field-work will probably be completed by December 1. On September 14, I found it necessary to relieve Colonel Ulffers, and to place Mr. Gorham P. Low in charge of the survey.

I cannot terminate my supervision of the works for the improvement of the rapids of the Mississippi River without again calling attention to the necessity for their completion at the earliest possible day.

There is no physical reason whatever why this should not be done by the end of the working season of 1871, and I do not hesitate to say that considerations of economy and good management, as well as the interests of commerce and navigation, demand that the necessary means should be provided without further delay.

Very respectfully, your obedient servant,

J. H. WILSON,

Lieutenant Colonel and Brevet Major General, U. S. A.

Brigadier General A. A. HUMPHREYS,

Chief of Engineers, U. S. A., Washington, D. C.

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 miles. 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 1 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. Concrète 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, 1 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.