In a very little while, measured by the swift flight of time in this era of rapid solution of transportation problems, the huge railway car ferries on the Detroit River will have passed from the traffic life of the busy stream. For many years these powerful steamers have transported the enormous freight tonnage and millions of travelers across the border between the two countries. The five trunk linesthe Michigan Central, the Grand Trunk System, the Wabash, the Pre Marquette, and the Canadian Pacificoperate no less than ten of these car floats. When the Detroit River tunnel, one of the most important railway enterprises of the present time, is completed, the through "limited" and express trains and the long heavy freights of all the trunk lines will pass below the bed of the river, and rise to the surface of another country in six to seven minutes. By the present system, about thirty minutes is lost in ferrying and switching each express train, and from four to seven hours in handling through freights; while perishables, which are given the preference over all other classes in quick ferriage, do not get under way again within three hours. In winter, when the ice floes, brought down from Lake St. Clair by the swift current, often jam the river from bank to bank, the big steamers frequently become fast in the stream; and the delay from this cause to fast passenger service between the East and the West sometimes amounts to from three to twelve hours. The saving in time and expense of operation in moving the heavy traffic across the river through a double-tracked tunnel, over the slow and uncertain ferry system, is deemed by the Michigan Central officials, in view of the ever-increasing tonnage of the road, of sufficient moment for the expenditure of $10,000,000 in the construction of the international tunnelway. About three years ago the project was taken up by Mr. Henry B. Ledyard, then president of the Central, and through his untiring efforts the board of directors authorized the construction of the tunnel, and also the organization of the advisory board of engineers to carry out the great undertaking. The advisory board was appointed in June, 1905, and was composed of W. J. Wilgus, then chief engineer of the New York Central and in charge of the electrification of the New York city terminals; H. A. Carson, consulting engineer, who designed and built practically all of the Boston subways; and W. S. Kinnear, chief engineer of the tunnel in charge of construction. Instead of digging parallel bores through the tough blue clay far below the bed of the river, by means of shields driven by hydraulic rams, a great trench has been dredged out of the bottom of the river, in which are being sunk successive tubes of steel, 23 feet in diameter and 260 feet long, secured together by transverse stiffening diaphragms of steel at every eleven feet of their length. These tubes form the waterproofing of the tunnel proper, which consists of a solid ring of concrete, two feet in thickness, formed within the tubes. The width of the river between dock lines is about half a mile, and the subaqueous section of the tunnel, or part entirely under the river, will consist of ten of these twin tubes with a total length of 2,622 feet. Along the bottom of the trench, rows of piles have been driven and capped, to form a bearing for the tubes. The tubes are built at the shipyard of the Great Lakes Engineering Company at St. Clair, forty-eight miles away. The ends of the tubes are "plugged" with stout wood bulkheads, to render ther - watertight. Then they are launched into the river sideways, very much as lake ships are launched. Floating lightly on the water, and drawing no more than six feet, the tubes are towed by a tug down the river to the place where they are to be sunk. On top of the tubes and near each end are two air cylinders, ten feet in diameter and sixty feet long, strapped securely to the tube diaphragms, and these serve to regulate the settling of the tubes, as they slowly fill with water, which is admitted at the will of the engineers through gate valves in the bulkheads. There is also provided at each end a detachable upright, firmly braced to the section and of sufficient length to indicate the position of the tubes when they have been entirely submerged. These uprights also show the engineers the exact position of the tubes when they are resting on the piling, eighty feet below the surface of the river, and act in adjusting them in their position laterally, so as to bring the sections into alignment. The uprights extend about ten feet above the water when the section is in place. After all is prepared and proper precautions have been taken to check the least deviating movement, the gate valves are opened, and the tubes slowly settle into position. Each tube as constructed in the shipyard is provided at one end with a sleeve, which is slipped over the end of the adjoining tube already sunk and in position. The sleeve is fitted with a flange, which is bolted to a corresponding flange of the other tube, a rubber gasket being placed between the two. A similar gasket is slipped in at the inner end of the sleeve, bearing up against the edge of the other tube. When the bolts are in place and all is ready, divers turn up the nuts, thus squeezing the rubber gaskets together between the ends of the tubes to form a tight joint. An annular space of three inches by eighteen inches is thus formed all around the tube at the joint, which is then filled with a grout of pure cement. To this end each sleeve is provided on the top with two small pipes, flexible at the joints and leading up to the cement scow floating above. The water in the space is then pumped out, and if the least leak occurs in the main joint, there is more work for the divers in bolting up. When the joint is absolutely watertight, pure cement is pumped into the space through one pipe and continued until it comes out through the other, which is evidence that the space is completely filled. The water in the tubes is now pumped out and the inner bulkheads removed, leaving the space clear and dry to the outer bulkheads. Concrete gangs now come on the scene, and, pushing their big half circular wood forms along into the new tubes, proceed to build up the tunnel itself, which is of solid concrete varying in thickness from two to five feet. The concrete tube is calculated to be of sufficient strength to withstand all strains and vibrations of the heaviest trains, the steel tubes serving as waterproofing protection, while the outer covering of concrete in turn is the steel tube preservative. On each side of the lower section of the tubes there are benches of concrete four feet high and two and a half feet wide at the top, to serve as passageways and places of refuge for the trackmen. When the concreting is completed there is a clear head room of eighteen feet from the tops of the rails to the center of the arch. Out in the stream are the cement scows, fitted out with the latest concrete mixers and with huge cranes and other devices for the rapid handling of the material from the lighters alongside. The scows are anchored as immobile as is possible in the swift current of the river, which is constantly churned into choppy waves by hundreds of passing freighters and excursion and ferryboats plying the busy stream. By means of hoppers placed at the top of long vertical delivery pipes, the concrete, as it is prepared, is deposited in the trench exactly where it is needed, and comes in contact with the water only when it is spread over the surface of the gravel bed which was prepared for it. As the work goes on, the concrete is held in proper form about the tubes by three-inch oak planking, firmly braced and backed up with clay and river slime from the dredges, working in the trench farther out in the river. Concrete is also chuted down between the tubes and continued up over them for five feet, thus encompassing them in a solid monolithic mass. The trench is then filled around the tunnel, and the top is covered with riprap. The construction of the approach tunnels is proceeding on lines well established by the best engineering practice; and this part of the undertaking is a huge task of itself. Two shafts were first sunk at the river banks, one on each side, and from these excavating for the center wall was carried on inland as far as other shafts, and from them to the portals. Concrete gangs followed, building up the center wall, and when this was completed, the bores were pushed forward by a modification of the shield methods of the New York tunnel work, the change being necessary because of the tough clay of the under stratum. The shafts near the river will be permanent, and they are lined with double walls of concrete. They will serve to ventilate the tunnel, and as trains move in each tube only in one direction, a constant circulation of air will be maintained. Electricity will be the motive power used in hauling trains through the tunnel, and current from the power plant of a local concern has been arranged for. Only a small transforming station will be needed to convert the alternating current, commercially supplied, to direct current for the locomotive motors. For the operation of the tunnel eight powerful electric locomotives are being constructed. It will be brilliantly lighted with electric lamps, and the walls will be clean and bright, for there will be none of the gas and soot that fill tunnels operated by steam locomotives A system of block signals will be installed, and so arranged' that no train or locomotive will enter either tube until the train ahead of it has passed beyond the summit on the other side.