At Crieff, in Perthshire, there occurs a series of low hills running parallel to the Grampians. These hills consist of old red sandstone and greywacke. On one of them, the Cnock, the village of Crieff is built. Upon the south-east side of this hill, towards the southern extremity, not far from the summit, there are deposited a number of boulder stones of syenitic granite. The largest of these is called the cradlestone. It is nearly spherical, quite smooth on the surface, and 29 feet in circumference. It has been split in two by lightning, (according to the tradition of the place,) and one of the fragments has made one complete revolution down the hill and then stopped. The weight of this boulder is about 30 tons. The nearest mountains of syenitic granite, are those in the neighbourhood of Bennevis, distant more than 60 miles north-west [...]
In the memory of men still living, two well-known weavers, named James Livingstone and James McLaren, lived in Barnkettick, at the west end of the town. Livingstone was a through wag, and McLaren was somewhat of a simpleton. Livingstone was in the habit of telling his neighbour all sorts of extravagant stories about ghosts and witches. The facility with which the latter fraternity could turn themselves into hares and scamper about was an accepted fact, which McLaren as truly believed as his Bible.
The Rocking or Cradle Stone on the brow of the Knock, behind the town, was supposed to be of Drudical [sic] origin, and for ages drew forth the fear and wonder of the natives. A belief prevailed that something valuable was buried in its foundation, and worth lifting, if it could only be got at.
The story's told at great length. Basically, Livingstone gets a few of his mates involved, and they turn up early with snares and 'squibs'. When the two friends start digging, "a strange unearthly sound came up the hill, and on looking round, a ball of fire was seen careering through the underwood. McLaren felt queerish and almost speechless." But Livingstone said they were only bits of falling stars. McLaren thought otherwise, that it was something to do with the Monzie witches. When Livingstone yelled that he smelt brimstone, McLaren rushed terrified down the hillside, scaring rabbits and hares that then got caught screaming in the snares. He makes it home but Livingstone clearly doesn't know when to stop and ties a live hare to the bed, which McLaren of course interprets as a witch.
The RCAHMS record says the Cradle Stone is a huge boulder that's been split in two. Surely it's called the Cradle Stone because it rocks / rocked at some point? but in a mention in PSAS (v45/1910) it says "the local story is that the Cradle Stone is where the babies came from!" Maybe that's a kind of back-explanation with a fertility related twist?