Carrig Slic is a lost stone, which I've tried on numerous occasions to find. By the time it was engulfed by the forestry plantation (possibly during the 1950s) it had already fallen, and nobody really knows what happened to it after that. Here's what little I could glean from records at the NMRW:
On the southern side of Mynydd March, approximately 150 yards north of Lluestfach Farmhouse. It stands on land sloping westwards and on the northern side of a col.
Now prostrate, but was standing in living memory. 9' 6" in length. Has drill marks on it from failed attempt to convert to gate post.
The grid reference that we have for the stone is only approximate (SN71908355). In 2003 the forest in this area was clear felled, but sadly this didn't reveal the stone. If it lies slightly to the south then it may be buried under a forestry track, or if it's a bit further south it may still be in remaining forestry. The name Carrig Slic means 'the slippery stone', which seems wholly appropriate.