Hi June, I suspect small sarsens are found in many of the monuments around Avebury. Windmill Hill has them in the ditches as does the Palisaded enclosures, in this instance they were used as packing stones round the posts.
Dean Merewether in his excavation of 1849 seems to have come across them, to quote Pollard;
"Observations during the 1849 excavations suggest this mound was edged with sarsens"
Edging or kerbing with stones around barrows can be found round this part of Somerset, Wick barrow had a stone wall built around it which was covered with earth as soon as it was built....