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of Amiens Street Terminus, Dublin.
1876 The Great Northern Railway of Ireland (GNR(I) or GNRI) was an Irish railway company formed by the merger of the Irish North Western Railway (INW), Northern Railway of Ireland, and Ulster Railway. The Ulster Railway was the GNRI's oldest constituent, having opened between Belfast and Lisburn in 1839 and extended in stages to reach Clones in 1863. The Northern Railway of Ireland was itself formed by a merger of the Dublin and Drogheda Railway (D&D) with the Dublin and the Belfast Junction Railway (D&BJct). 
The Ulster, D&D and D&B Jct railways together formed the main line between Dublin and Belfast, with the D&B Jct completing the final section in 1852 to join the Ulster at Portadown. The GNRI's other main lines were between Derry/Londonderry and Dundalk and between Omagh and Portadown. The Omagh-Portadown link allowed GNRI trains between Derry/Londonderry and Belfast to compete with the Belfast and Northern Counties Railway, and both this and the Dundalk route gave connections between Derry/Londonderry and Dublin. These main lines supported the development of an extensive branch network serving the southwest half of Ulster and northern counties of Leinster. The GNRI became Ireland's most prosperous railway company and second largest railway network.
In its early years, the GNRI had closely imitated the image of its English namesake, adopting a pleasant apple green finish for its steam locomotives and a varnished teak finish for its passenger coaches. Later the company adopted its famous pale blue livery for locomotives, with the frames and running gear picked out in scarlet.
1908 The line owned is 542.25 miles in length. 
1924 The Railways Act 1924 provided for the amalgamation of all railways wholly within the Irish Free State. Only cross-border railways, most notably the Great Northern Railway, remained outside the new company.
1948 The Ulster Transport Authority acquired that portion of the Great Northern Railway within Northern Ireland.
1958 Under the Great Northern Railway Act, which became operative on 1st October 1958, the Great Northern Railway rail and road services within Eire were amalgamated with Coras Iompair Eireann. The cross-border rail service was worked as a co-ordinated service between Coras Iompair Eireann and the Ulster Transport Authority.