to access the South Eastern Railway via the East London Railway (ELR), an Act of Parliament was obtained to complete the circle and link to the ELR. After an official opening ceremony on 17 September and trial running, a complete Circle line service started on 6 October 1884. The Metropolitan Railway had been extended soon after opening, reaching Hammersmith with the Great Western Railway in 1864 and Richmond over the tracks of the London and South Western Railway (L&SWR) in 1877. The Metropolitan & St John's Wood Railway opened as a single track branch from Baker Street to Swiss Cottage, and this was to become the Met's most important route as it expanded north into the Middlesex countryside, where it stimulated the development of new suburbs. Harrow was reached in 1880, and the line eventually extended as far as in Buckinghamshire, more than from Baker Street and the centre of London. From the end of the 19th century, the railway shared tracks with the Great Central Railway route out of . By 1871, when the District began operating its own trains, the railway had extended to West Brompton and a terminus at Mansion House. Hammersmith was reached from Earl's Court and services reached Richmond, Ealing, Hounslow and Wimbledon. As part of the project that completed the Circle line in October 1884, the District began to serve Whitechapel. As a result of the expansion, by 1898, 550 trains operated daily. Services began running to Upminster in 1902, after a link to the London, Tilbury & Southend Railway had been built. Electric underground railways (1900–1908) Deep-level tubes In 1869, a passage was dug through the London Clay under the Thames from Great Tower Hill to Pickle Herring Stairs near Vine Street (now Vine Lane). A circular tunnel was dug , using a wrought iron shield, a method that had been patented in 1864 by Peter William Barlow. A railway was laid in the tunnel and from August 1870 a wooden carriage conveyed passengers from one side to the other. This was uneconomic and the company went bankrupt by the end of the year and the tunnel was converted to pedestrian use, becoming known as the Tower Subway. Construction of the City and South London Railway (C&SLR) was started in 1886 by James Henry Greathead using a development of Barlow's shield. Two circular tunnels were dug between King William Street (close to today's