made an angle of about 5° with the axes of the piers. Through the west draw-opening the general direction taken by floats was nearly parallel with the axes of the piers. The change in direction between low water at the time our first observations were made, and at high water when our second observations were made, was considerable. But at each stage one of the draw-openings was available, with current direct through it. At low water the left draw-opening was the better, and at high water the right opening was the easier to run. From the right bank, at time of high water, the current sets toward the center of the bridge, so that floats put in opposite the span next Dubuque, 1,000 to 1,500 feet above the bridge, passed through the fourth span from the Iowa shore at an angle of 25° with the axes of the piers. This was caused by the current setting out of Seventh street slough immediately above the bridge. The current through the long span next to the right draw-opening was practically parallel with the axes of the piers. The span next the draw on the left or Illinois side cannot be used for rafts floating with the current on account of a bank built out, and formerly used as a transfer landing, about 400 feet above the bridge. If, from this point, a line be drawn in the direction of the current (nearly parallel with the piers) it will cut off 150 feet of this span, and this is practically equivalent to reducing the width for raft navigation by that amount, which renders the whole useless. This span, if its full width had been made available to rafts, would have been very useful. The passage-way provided for steamboats is as good as a draw-bridge at the site permits, unless by proper rectification of the Illinois shore it had been made so that one draw-opening could be placed next to it. This would have been especially desirable at this point, which is one where the wind is very troublesome to boats passing the bridge. It would have brought the 250-feet span, which is on the right of the draw-opening, 100 feet nearer the center of the stream, and rendered its use by rafts more easy. ALTERATIONS TO LESSEN OBSTRUCTIONS TO NAVIGATION. Sheer-booms.-The board of engineers recommended that a sheer-boom 1,200 feet long be placed with its lower end abutting against the pier on the right of the Iowa 250-feet span, and to extend up stream on prolongation of the axis of the pier, so that it can be swung to sheer rafts into the right raft span, or into the right draw-span. Those representing the raft interest before this board asked for booms on other piers, but as they would interfere with the passage of the bridge by steamboats, they were not recommended. Lengthening of left rest pier.—This pier should be extended up stream 800 feet in the direction of the current. This extension should be 4 feet above high water, and built of timber with its sides smoothly planked. If this were built boats could "round to" and drop through the bridge alongside of it avoiding the now frequent delays on account of darkness or high winds. HIGH BRIDGE. This place is one of the most favorable for a high bridge on this part of the river. The left bank is high close to the shore, and high land opposite is but one mile distant. The provisions for clear headway of 55 feet above high water, which is 77 feet above low water, would give an opportunity for all boats to pass under it that can pass the bridge at Saint Louis. (See Chap. III.) PROPOSED PONTON BRIDGE AT DUBUQUE, IOWA. An act of Congress approved March 3, 1875, authorized the construc. tion of a pile and ponton bridge across the Mississippi River at or near the city of Dubuque, Iowa. The proposed plan and location were submitted to the Secretary of War. A board of engineers-Col. J. N. Macomb, president-was convened to consider and report upon them. This board objected to the first and second locations, which were near the present bridge, but approved of the third, which was at Eagle Bluff, 2 miles above. (See Annual Report of the Chief of Engineers for 1876, Part II, pp. 308, 313.) This bridge has not been built. CLINTON RAILWAY DRAW-BRIDGE. (Opened for railway travel in January, 1865.) Authority. This bridge was built by the Albany Bridge Company under authority of the legislatures of the States of Illinois and Iowa. The portion over the east channel and Little Rock Island was built and in operation some time previous to the building of that portion over the west channel, the transfer over this being made by ferry. It was declared a post-route by act of Congress approved February 27, 1867. DESCRIPTION OF RIVER AND VALLEY AT THE LOCALITY. In connection with this bridge we shall consider the question of a high bridge at Fulton and Lyons, about 2 miles up the river, and our description will therefore embrace that locality. The high ground at Fulton, on the Illinois side, extends only about a mile along the river. The river here is about 3,500 feet wide, and all confined to one channel. About one mile below the high ground the bank of the Illinois side or left bank is composed of a low stratum of Jime-rock for a short distance, and opposite this the river at low water is reduced to a width of 2,400 feet, part of which is occupied by a dry sand-bar. This place is about a mile above the bridge, and on many accounts presents a good site for a bridge (although the banks are not above overflow) because the deep water is constantly next the rocky shore. At the site of the bridge the water-way is divided by Little Rock Island. The main channel is on the right or Iowa side of this island, and does not change. The island is composed of stratified limerock, a little elevated above ordinary overflow. Between the island and the left bank the water-way is shoal and much of it occupied at low water with dry sand-bars and willow-islands. The main bank on the Illinois side is alluvial, and subject to overflow. On the Iowa side it is rock in place, but not above extreme high water. Little Rock Island is in the jurisdiction of the State of Illinois, the middle of the west channel being the dividing line between the States of Illinois and Iowa. The width of the valley submerged at high water is about 2 miles. The slope of the water is about 0.27 feet per mile at low water. The current is gentle, being 13 miles per hour when the water is 2.5 feet above low water. With the water 10.7 feet above low water it is about 3 miles per hour in the main or Iowa channel. The rise from low to high water is about 19 feet. SURVEYS MADE. A survey of the Mississippi at this bridge was made by me in October, 1866, at a time of ordinary low water, and all the information that could be obtained at this stage of water was secured. Both banks were meandered from Fulton and Lyons down about one mile below Clinton, the river sounded, and current observations taken at the bridge. Current observations were again made here in May, 1867, at time of high water, and again in November, 1868, when the water was low, at the time of the rebuilding of that portion over the east channel. DESCRIPTION OF BRIDGE. (See Diagram 18.) Commencing on the left or Illinois shore, there is 1,390 feet of wooden trestling in the approach to the bank of the river; then there were at first 7 spans of wooden trusses, each 200 feet long; then a causeway 583 feet long across Little Rock Island to the Iowa channel. The Illinois channel thus bridged was crossed at an angle of 74° with the general direction of the channel, so that these spans of 200 feet from centers were practically narrowed to about 190 feet, measured at right angles to the current, and this was decreased by the width of piers and protection of riprap to 160 feet. The riprap protection was raised to about 3 feet above low water; the available width above this stage was practically about 180 feet. The span next to the Illinois shore, the one used by rafts, had this width available for all stages above 3 feet above low water. The headway at time of high water was about 8 feet under these spans. At the time of our survey, in 1866, this bridge was in very bad condition, the piers, built with a core of concrete, were cracked in several places, and to support the spans temporarily various devices had been resorted to. The trusses, which were of that pattern known as McCallum's, were decayed in many parts, and a large number of the diagonals were split and broomed where they abutted against the angle blocks. In 1868 and 1869 this part of the bridge was entirely rebuilt; the first span next to the Illinois shore was replaced by an iron truss; the remaining portion, 1,200 feet to the abutment on Little Rock Island, was replaced by 8 iron spans of 150 feet each; the new piers were smaller, 9 feet wide on top, of masonry, resting upon piles. The 200 feet span and the two adjoining 150 feet spans were built by the American Bridge Company, of Chicago, on the Post pattern. The next two spans were built by the Detroit Bridge Company, Detroit, Mich.; the next two, by the Phoenixville Bridge Company, of Phoenixville, Pa.; the next two, by the Keystone Bridge Company, of Pittsburgh, Pa. The last six are of the Pratt truss pattern. The bridge over the Iowa channel, built in 1864-'65, consists (com. mencing at Little Rock Island) of one span 174 feet and 200 feet of wood; then a pivot draw-span of iron (Bollman) 300 feet over all, with an opening on the east side of pivot-pier of 119 feet at low water, and one of 128 feet on the west side; then a span of 174 feet to abutment on the Iowa shore (this is of wood); then a short piece of embankment. Substructure. The piers in the east channel, before referred to, are of masonry, resting on a grillage which rests upon piles sawed off below low water. The pivot-pier and guard-rests are combined in one large crib about 400 feet long and 35 feet wide. The left rest-pier is also a crib filled with stone, 140 feet long and 25 feet wide. The excess in width |