tunnelling never started, likely for economic reasons. This proved to be serendipitous, as the freestone was proved to run at a depth of under the Forth when the Kinneil and Valleyfield mines were joined in 1964. Other tunnels through similar material attempted at the time failed, notably an attempt to tunnel under the River Thames between Gravesend and Tilbury. In 2021, the Scottish Greens proposed a long rail tunnel from Kirkcaldy to Leith which would bypass the Forth Bridge. If built, it is suggested that it would cut journey times from Edinburgh to the north by 25 minutes, while adding capacity to the railway network. Early bridge proposals Bridges were possibly proposed as early as 1740 or 1758, but no records have been found. The materials available at the time, namely stone and wood, offered a limited maximum span of around 30 metres, making construction of such bridges in deep water unfeasible. After Henry Cort invented puddling in 1783 as a method of producing large quantities of high-quality iron, such bridges could again be considered. Scotland had four wrought-iron footbridges by 1817, with the longest spanning a distance of . Thomas Bouch Thomas Bouch was a railway engineer responsible for designing and constructing relatively cheap branch lines at a capital cost allowing them to pay their way; eg the Darlington and Barnard Castle Railway (completed 1856), the South Durham and Lancashire Union Railway (completed 1861), the Eden Valley Railway (completed 1862), and the Cockermouth, Keswick and Penrith Railway, (completed 1864, with 135 bridges). He made considerable use of lattice girder bridges with piers of (conventional) masonry or cast iron lattice. Bouch returned repeatedly to the problem of bridging the two great East Coast firths, the Forth and the Tay. When authorisation was given to bridge both firths, Bouch was selected to design both bridges. The first Tay Bridge (designed by Gough) was authorised in 1870 and completed in 1878. Bouch was knighted in June 1879 soon after Queen Victoria had used the bridge. But after the Tay Bridge disaster of 1879 Bouch was blamed for design faults including not allowing for high wind pressure and also for poor quality of various items (e.g. lugs or cross bracing) although the three engineers involved could not agree on many aspects of the report. Bouch's design for a suspension bridge to take a railway across the Firth of Forth, had been accepted and