However, reaching the location involved a tunnel on a steep gradient, and wagons were hauled up and lowered by rope operation controlled by a steam engine.

[2] A report prepared for him by his factor John Grieve proposed a railway from his pits to the city, with a branch to Fisherrow, a fishing harbour near Musselburgh.

4. c. lxxi), on 27 June 1834, authorised a further £54,875 to build branches to Fisherrow, and "allowing a certain amount of passenger traffic by horse-drawn railway coaches".

The route ran via Millerhill village and Hardengreen, crossing the North Esk on a bridge 60 feet (18 m) high, and the main line was about 10+3⁄4 miles (17.3 km) long.

The terminus at Dalhousie Mains is referred to as "Eskbank" by one source,[6] but that name was not applied until after takeover of the line by the North British Railway.

He constructed an extension to the pits from the Edinburgh & Dalkeith Railway (E&DR) terminus at Dalhousie Mains at his own expense, a distance of 1+1⁄2 miles (2.4 km).

[5] In March 1835, the E&DR opened a branch (authorised by the Edinburgh and Dalkeith Railway Act 1829)[6] from Niddrie to a terminus at Constitution Street in Leith.

[4][5][11][14][note 1] Carter gives the point of divergence as "Niddrie North Main Colliery", and he adds that the total length of the branches amounted to 6+1⁄2 miles (10.5 km).

[10] The E&DR made a branch from the south end of the North Esk viaduct curving round east and north-east into Dalkeith, opening in the autumn of 1838.

It afterwards takes a southerly course by Miller Hill Row, to within half a mile of the west side of the town of Dalkeith, where it crosses the North Esk River; thence, to the banks of South Esk River, at Dalhousie Mains, near Newbattle Abbey, from whence, the last act [i.e. a second Act of Parliament] enables the company to extend it to Newton Grange.

There is a branch from Wanton Walls to Fisher Row Harbour, on the Firth of Forth; another from Cairney to the collieries situate on the east side of the Esk, at Cowpits, near Musselburgh ; and another by a subsequent act, which extends to Leith Harbour.Whishaw says The main line, which runs from the Edinburgh station to South Eske, is level for about half its length; and the remainder has an inclination of 1 in 234, the whole distance being 8+1⁄4 miles … The Leith branch is level for about one-third of its length; and the remaining portions have inclinations of 1 in 300 and 1 in 69 respectively, the whole length being 4 miles … The Musselburgh branch [i.e. Fisherrow] is altogether on an inclination of 1 in 51+1⁄2 … In the main line we counted seven bridges over the railway, four bridges under, six level road-crossings … the main line being double throughout … There is one tunnel 572 yards in length, which is on the Edinburgh inclined plane … the Tunnel is lighted by twenty-five gas lamps … The gauge is 4 feet 6 inches … the rails are of the fish-bellied form, weighing 28 lbs to the yard … the whole way is laid with freestone blocks … Near [South Eske] station is a long wooden bridge, which carries the Marquess of Lothian's railway over the river Eske.

It is worked by two low-pressure condensing engines, with cylinders 28 inches diameter, stroke 6+1⁄2 feet; average working-pressure, 5 lbs … consumption of fuel 2+1⁄2 tons per diem … About 30 tons gross is the usual load drawn up, and five minutes the time occupied; the descending loads draw out the rope after them … The signals from the bottom of the incline are given by an air-tube, about 3⁄4 inch diameter, with a small bell in the engine-house.

[2] Passengers had hardly been considered when the railway was being planned, but a businessman, Michael Fox (who had been dynamic in managing coal deliveries in the city) put "an old stagecoach on the line and on 2 June 1832 began a service of three return trips a day between St Leonards and the North Esk depot".

"[5] During 1839 during evidence being given in Parliament, it was stated that the railway did not issue tickets because there were so many informal stopping places, and that some passengers declined to reveal their intended destination.

The trains-guards are also constables... Each guard carries a bugle-horn, which he sounds lustily as occasion requires.The Company's stock of carriages at present consists of thirty-four passenger-carriages [and] eight luggage-vans...

Then, as now, people took advantage of the Fast Days [public holidays] to spend a few hours outside the city, and it was no uncommon thing for the Dalkeith Railway to bear away four or five thousand pleasure-seekers on such occasions.

The passenger coaches were a sort of hybrid between the old-fashioned stage-coach and the modern [horse-]omnibus, and in summer the outside seats were the most popular.The north British Railway produced a map in 1844, which showed intermediate stations on the Edinburgh and Dalkeith system.

[6] The NBR did the same to the Marquis of Lothian's Waggonway from the South Esk bridge to Arniston,[note 3] forming a through route from Edinburgh to Gorebridge, opening on 7 July 1847 for goods and a week later for passengers.

The North Bridge station was much more convenient for the city and for connecting trains, and usage of the original St Leonards terminus for passengers declined steeply: it closed on 1 November 1847.

[8] The NBR took the opportunity to build a branch to Musselburgh itself: the harbour there did not suffer so badly; the line crossed the River Esk, and opened in 1847.

During the British Railways Modernisation Plan of the early 1960s, there was a need to build a large modern mechanised freight marshalling yard to concentrate goods train activity for the Edinburgh area, and this was situated at Millerhill, on the original E&DR main line a little south of the Niddrie junction.

The St Leonard's terminus remained in use for coal and goods traffic until 1968; the depot warehouse dating from the 1830s with its characteristic columns and beams has been preserved.

[8] The bridge over the North Esk on the original main line is a fine single-span semicircular ashlar masonry arch with a span of 65 feet (20 m).

[8] When the Marquis of Lothian built his waggonway southwards from the Dalhousie Mains terminal of the E&DR, he had to cross the South Esk river; he did so by a viaduct consisting of 24 spans of timber with three pointed arches in cast iron.

It was superseded when the North British Railway were extending southwards; they replaced it with a 23 span masonry viaduct with brick arch rings, completed in 1847 and still in situ.

[8] Part of the line has been converted to a cycle path, connecting central Edinburgh, at Newington and St. Leonard’s at its west end, with Duddingston, Niddrie and Craigmillar to the east.

The name The Innocent Railway entered the history books and the legend grew that the line was so called because it never killed or injured a passenger.

Robertson says: Its familiar and affectionate soubriquet of the "Innocent Railway" was not due, unless inaccurately, to the legend that no-one was ever killed on it, but rather to an air of old-fashioned unreality which stood by the leisurely horse-drawn tradition long after it had been abandoned elsewhere.Robert Chalmers, who coined the nickname, gently enjoyed himself at its expense: By the Innocent Railway you never feel in the least jeopardy; your journey is one of incident and adventure; you can examine the crops as you go along; you have time to hear the news from your companions; and the by-play of the officials is a source of never-failing amusement.Robertson goes on to observe that a driver was killed in 1840 and two children were killed in 1843 and 1844, citing Parliamentary Papers 1841, 1843 and 1846.

Among its engineering features were an early tunnel, a cast iron beam bridge and an outstanding timber viaduct on masonry piers.

The viaduct at Thornybank, Dalkeith was finally demolished in the 1960s.In November 2021, a Red Wheel plaque was unveiled at the Holyrood Distillery, on the site of the former St Leonards station, to mark the railway's importance.