moyraza
That is a very fine medal to have, and you should treasure it. The militia system in Natal and Zululand consisted of Reserve Regiments that were called out in time of need, and, since the end of the Anglo-Boer War, they were backed up by Reserve units centred on smaller outlying towns.
Melmoth is in Zululand and was in the heart of the area where the second phase of the 1906 Natal Rebellion took place. The Melmoth Reserves would have been backing for the Zululand Mounted Rifles, which was one of the Reserve Regiments most heavily engaged in putting down the Rebellion. Five of the eight Distinguished Conduct Medals awarded during the Rebellion went to men of the ZMR.
The Natal Rebellion Medal was awarded to 57 men of the Melmoth Reserves, 25 of them with the 1906 clasp , like that of your GGF, and 32 without the clasp. The latter were for men who served for only a short time. Since your GGF was the unit Sergeant-Major, he must have been a respected man, probably with some prior military service. Perhaps he came to Natal as a soldier in the Boer War and stayed on afterwards, which was the case with many British soldiers.
I do not have any records to show what the Melmoth Reserves did during the Rebellion, but I suspect the men were an active 'home guard', since they were in an area mostly populated by Zulus who might have been supporters of the rebels. I will do some checking to see if I can find out more about the Reserves and your GGF.
Brett