'Near to the entrance to the Glen were the grassy embankments of a Roman Camp, but a feature of the valley that interested me more than this relic of the dim past was a great boulder about a mile beyond. It stood a little aside from the highway, and a much used path leading to it was evidence that it had many visitors. What the attraction was, I could not have conjectured, had I not heard its story previously. It had a smooth, rounding top, and rose above the ground to a height of seven or eight feet. At its base lay three heavy stones, the largest about the size of a peck measure.
It was a common custom among travellers who happened into Glen Urtach to try 'Saddling the Mare' that is, to attempt putting the stones up on the boulder. They slid off with surprising ease, and few persons had the strength or cleverness to lodge all three. Still it was allowable to boast, even if you only succeeded with the two smaller ones. That the sport was a popular one was attested by the battered whiteness of the top of the boulder.' The Land of Heather. Clifton Johnson (1903).
The above quote attests to the tradition of Saddlin the Mare when passing through the Sma' Glen. There were three stones of increasing weight to place on the top slope of the stone without falling off. The route through the sma' glen was a drovers road so the tradition may derive from ancient times.
There is a moderately sized stone at the base of the rock so it may be one of the original 'saddles'. It is interesting that a stone is 'saddled' on top of the rock in Andy's pictures so the tradition appears to be continuing.