Cist slabs with holes in the corners

[RedEarth]

I've come across a fairly random reference to a discovery of burials, possibly in cists, although it is quite vague, beneath what appear to be quite neatly dressed sandstone slabs. There were three slabs over at least one of the burials, each about 1 1/2 feet square, and each with four holes, one in each corner. A couple of stray skulls were also found nearby. The discovery is within the precinct of a medieval abbey, but not near the location of other known burials, and the 'cists' were possibly orientated north/south.

Does this sound even vaguely familiar to anyone? Just curious to know what date they might be.