Jon
In Chamberlain and Droogleever's "The War with Johnny Boer" there is reproduced on p.207 a letter from a Cpl. Warby in A Sqn., ILH who was on the Mafeking relief. Regarding the ILH's journey, Warby says "We led (the relief of Mafeking) by marching from 16 miles North of Ladysmith to Mooi river, then travelled to Durban, took a steamer to Cape Town and train to Kimberley". I think it is reasonable to assume that the Fusiliers made the same journey at about the same time. Another letter writer (Tpr. Warburton of the same ILH Sqn.) says that "Just a month from the day we left Durban ..... after some stiff fighting, relieved the besieged town". So that gives some idea of the length and time of their journey to get to the assembly point at Kimberley.
Regarding the Fusilier Coy., Stirling simply says (p.93) that "After the relief of Ladysmith, the 5th and 6th Brigades (now Xth Div) ..... in preparation for the relief of Mafeking and the occupation of the Western Transvaal .... was brought around to Cape Colony".
There is no doubt that the composition of Mahon's Southern column was intended to reflect the unity of the Empire's components.
Regards
IL.