More information Rhiannon; quoted from Welsh Saints by Breverton
"Twrog ab Ithael Hael founded Llandwrog in Caerns, also a couple of others, At Maentwrog, a huge stone different to local rocks (possibly a glacial boulder) is attached to the angle of the church, and is known as Maen Twrog. It was supposed to have been thrown by Twrog from the top of the mountain of Moelwyn. Maen Llwyd is a standing stone in Glynllifon Park near Maentwrog..Probably Twrog's holy well is just a 100 yds from Maentwrog church"
There you are another stone throwing giant cum saint to add to the list...
p.s. went to the Golden Valley Reserve, Wick today and looked at the quarry there, the earth is stained bright red where the red ochre comes through - could it be that Wick Burial chamber people were trading in hard rock and ochre??