Many of the earlier mineral workings, and branches constructed to serve them, have ceased, and many local passenger stations in rural areas have closed.

In 1921 the G&SWR had 1,128 miles (1,815 km) of line (calculated as single track extent plus sidings) and the company’s capital was about £19 million.

The GPK&AR had anticipated constructing its authorised line and then the extension, but by 1846 there was a frenzy of competing schemes that threatened to destroy the company's core business.

Few of these were realistic, but the GPK&AR itself felt obliged to promote numerous branches, many of them tactical, in order to keep competing schemes out.

This period of railway promotion was followed by a slump, when money was difficult to come by, and these factors prevented the GPK&AR from bringing its Carlisle extension into reality.

Enthusiasm for a connection to English railways continued, however, and was intensified by the promotion of other schemes to link central Scotland and England.

Opposing promoters put forward a so-called central line via Carstairs and Beattock, that had the advantage of a shorter mileage, and the capacity to serve Edinburgh directly, but the disadvantage of much heavier gradients and running through a less populous area.

[3] Although this was described as a merger, the reality was that the penniless GD&CR was dissolved, its operation was taken over by the GPK&AR, and the latter company changed its name to the G&SWR.

Good enough as the results were, the long main line to Gretna was not producing much, due to the dominance of competing route of the Caledonian Railway, and business in general declined following the first half-year.

A pooling agreement was finalised in 1853 which mitigated some of the worst toll charges, but routing of goods traffic via the CR was made obligatory in many situations.

Mail, cattle, and soldiers had been conveyed that way, but reaching Portpatrick with a railway across difficult and sparsely populated land had been a challenge.

Encouraged by the CD&DR authorisation, at the end of 1856 promoters resolved to build a British and Irish Grand Junction Railway, 62 miles (100 km) from Castle Douglas.

The City of Glasgow Union Railway obtained Parliamentary authorisation on 29 July 1864; the capital was £900,000 with the G&SWR and the E&GR taking one-third of the shares each.

The line would run from a junction with the Paisley joint line at West Street[note 2] to Sighthill on the E&GR, with a new passenger station at St Enoch, a large goods station in land vacated by the University of Glasgow and a connection at West Street to the General Terminus goods branch on the bank of the Clyde.

[3] Construction was slow and costs overran heavily; on 12 December 1870 the first trains ran from Shields Road to a temporary central passenger terminus at Dunlop Street.

On 1 June 1871 the line was extended to Bellgrove, joining the North British Railway (NBR) there, and forming the north-south connecting link, which was heavily used for transfer goods trains.

In the 1890s it became obvious that expansion of St Enoch was essential, and on 18 August 1898 the Glasgow and South Western Railway Act 1898 (61 & 62 Vict.

The port developed and carried increasing volumes of goods, and passenger traffic for the Clyde ferries grew considerably.

This gave a quayside transfer to steamers at Greenock, and a price war with the established CR line broke out, eventually resolved with a traffic sharing agreement: the G&SWR received 42.68% of receipts.

Continuing from Girvan to Portpatrick, for the crossing to the north of Ireland was still an aspiration, but this section was the most difficult, and sparsely populated terrain.

After some false starts, friendly promoters put forward a Girvan and Portpatrick Junction Railway (G&PJR) obtained an authorising act of Parliament[which?]

The combined network formed the Portpatrick and Wigtownshire Joint Railway, purchased by a consortium of the interested larger companies, the G&SWR, the CR, the MR and the LNWR.

The canal was long defunct, and a new line was built passing under the bridge and running to Cart Junction, eliminating the conflicting move.

When the Caledonian Railway reached the town from the east in 1905, a non-encroachment agreement was activated and a few miles of line from Darvel to the Lanarkshire county boundary was transferred from the CR to the G&SWR.

The volume of mineral traffic heading for Troon and Ayr caused congestion in passing through Kilmarnock station, and a by-pass line on the south side of the town opened in 1902.

For a time a circular passenger service was operated from St Enoch via Paisley Canal, Potterhill and Barrhead Central.

Intended to open up remote coastal settlements between Ayr and Girvan it was promoted with the construction of the luxurious Turnberry Hotel.

It opened with two wooden masts built into the castellated telegraph hut, the tallest for running up and down a flag to signify if the main line north to St Enoch was clear and the second one slightly shorter to signal the trains for the Castle Douglas branch.With the opening of the Lockerbie branch into Dumfries in 1863 the pointsman's tower was removed from the junction beyond Albany Place and was re-erected on the summit of the slope at the deep cutting north of Dumfries station.

In 1971 the Princes Pier stub was connected to the Wemyss Bay line at Cartsburn Junction in order to serve the Clyde Port Authority container terminal.

This links Lady Octavia Park in Greenock, through upper Port Glasgow, Kilmacolm and past Quarrier's Village to Paisley.