That is a wall but there traces of quartz in it. I noticed that as well, climbed Ceapabhal later that day, magnificent views and with binoculars a hint of St Kilda to the west.
From Luskentyre down to Rodel is superb, going back next year to same place to look south making use of the ferry at Leverburgh :-) (We were based in Rodel and lived in a log cabin made by guys from Old Rayne)