The beginning of this story is apparently much sillier than the version already posted would hint at. Monty Python style silly. Unfortunately after that it just gets nasty.
A sanguinary encounter once took place between the Maclaurins of Auchleskin and the Buchanans of Leny, arising out of the following circumstance:
At the fair of St. Kessaig held in Kilmahog, in the parish of Callander, one of the Buchanans struck a Maclaurin of weak intellect, on the cheek, with a salmon which he was carrying, and knocked off his bonnet. The latter said he would not dare to repeat the blow at next St. George's fair at Balquhidder.
To that fair the Buchanans went in a strong body, and on their appearance the half witted Maclaurin.. told of what had occurred.. The warning cross was immediately sent through the clan, and every man able to bear arms hastened to the muster.
In their impatience the Maclaurins began the battle before all their force had collected, and were driven from the field, but one of them, seeing his son cut down, turned furiously upon the Buchanans, shouting the war-cry of his tribe ("Craig Tuirc*," the rock of the boar), and his clansmen rallying, became fired with the miri-cath, or madness of battle, rushed after him, fighting desperately.
The Buchanans were slain in great numbers.. [the story carries on as below..]
From p36 of The Scottish Nation, By William Anderson (1863).
*actually says Craig Tuire. But they mean Craig Tuirc.
Once on a market day a large number of armed Buclianans came over from Leny and quarrelled with the Maclaurins, the result being such a terrible conflict that only two of the Leny men escaped from the spot. The slaughtered Buclianans were thrown into a pool of the Balvaig River adjoining, and that part of the river is to this day called " Linn na Seichachan (the Linn of the Hides), where the corpses of the slain for a time stopped the course of the stream.
The two men who fled had only a short respite. They swam the river and made for home, but were pursued, one being overtaken and killed on the hillside about a mile from the market. A cairn marks the spot where he fell. The other, making for Strathyre, met his fate a little farther on, the spot being still known as "Stron-lenac," the Leny Man's Point).
This is the cairn then. The RCAHMS record says the OS visited it in the 1960s and described it as a low, grassed-over mound of stones, 3.0m in diameter and 0.3m high. "On top of this, a modern cairn, with many white stones, had been been erected. Whether or not this is a burial cairn could not be established but there are very strong local traditions agreeing with that by Gow".
Story from Gow, J M (1887)
'Notes in Balquhidder: Saint Angus, curing wells, cup-marked stones, etc',
Proc Soc Antiq Scot, 21, 1886-7, 83-4.
Gow also mentions (p87) some cupmarked rocks at Garnafuaran:
On the opposite or south side of the River Balvaig, on the farm ofGart-na-fuaran, there is a great number of huge water-worn boulders, which appear to have been brought down from the adjoining Glenbuckie in the Glacial period. They are of the coarse rock of the district, many of them with large veins and masses of quartz. About fifty yards east from the farm-house there is an immense boulder, 26 feet long, 18 feet broad, and about 12 feet high. It is on the roadside leading to Strathyre, and on the top, which slants slightly to the south, there are five cup-marks, and, as usual, of various sizes, the largest being 4 1/2 inches in diameter; and, as on the stone at Auchleskine, there are other shallow hollows, but these are not marked enough to be identified as cup-marks. The two end cups of the group are 30 inches apart from centre to centre and point due north and south.