Another modification of the parallel longitudinal trenches method was used in the construction of the New York subway. A narrow longitudinal trench was excavated on one side of the street near the sidewalk. Meanwhile the pavement of half of the street was removed and a wooden platform of heavy planks, supported by longitudinal beams which were buried in the ground, was substituted. Then small cuts underneath the car tracks were directed from the side trench and heavy beams or needles were placed in these cuts, which also reached the longitudinal beams of the wooden platform. The needles were wedged and blocked to the car track structure and the beams. They were temporarily supported by cribs built from underneath as the excavation progressed. When the subgrade was reached, vertical and batter posts were inserted to support the needles, thus forming regular timber bents underground. In the space thus left open the subway was constructed to the middle of the street. While the work was going on as described, another longitudinal narrow trench was excavated at some distance on the other side of the street. From this trench, the work of constructing the other half of the subway was carried on in the manner just described. After the work had been completed, the timbers removed, the voids filled in and the pavement of the street restored, another equal section was attacked on both sides of the street. =Transverse Trenches.=--The transverse trench or “slice” method of open-cut tunneling has been employed in one work, the Boston Subway. This method is described in the specifications for the work prepared by the chief engineer, Mr. H. A. Carson, M. Am. Soc. C. E., as follows:-- “Trenches about 12 ft. wide shall be excavated across the street to as great a distance and depth as is necessary for the construction of the subway. The top of this excavation shall be bridged during the night by strong beams and timbering, whose upper surface is flush with the surface of the street. These beams shall be used to support the railway tracks as well as the ordinary traffic. In each trench a small portion or slice of the subway shall be constructed. Each slice of the subway thus built is to be properly joined in due time to the contiguous slices. The contractor shall at all times have as many slice-trenches in process of excavation, in process of being filled with masonry, and in process of being back-filled with earth above the completed masonry, as is necessary for the even and steady progress of the work towards completion at the time named in the contract.” In regard to the success of this method Mr. Carson, in his fourth annual report on the Boston Subway work, says: “The method was such that the street railway tracks were not disturbed at all, and the whole surface of the street, if desired, was left in daytime wholly free for the normal traffic.”