I got round this by imagining that the Sligo & Donegal Junction grew out of a mineral railway from Garrison to Mullaghmore which with the growth of traffic and the limitations of Mullaghmore harbour led to an extension to Sligo Quay and a link with the M&GWR. In the early years of the 20th Century and the opening of the Donegal Railways Ballyshannon branch a further line was built from the north of Four Masters Bridge to the CDRJC terminus but with a connection to the GNRI which wanted a .piece of the action. The S&DJR.' s mineral traffic and that the majority of its shares were held by the Mining Company meant that it was profitable enough to to resist any attempts by the M&GWR, GNRI, MR and GS&WR to take it over. The line's terminus being over the Border meant that it didn't get included in the GSR. After WW11 the line remained independent but after the closure of the Garrison tip in the North, the company persisted with steam (even purchasing several fairly new but redundant GNRI locomotives) However in the early 1960's the railway turned increasingly to Irish Rail to run its services rather than purchase its own diesels.