In a photo from the 1974 excavations one of the tallest stones of the [url="http://www.themodernantiquarian.com/post/51678"]Trwyn Du[url] cairn shows several straight 'cut' marks. There is a group of three parallel lines and a pair of parallel lines. The nearest two lines of each group meet and form a very deep V. Most peculiar, as any other lines that appear on the stone are shorter and perpendicular to these markings. I think the top of the stone in question can be seen in stubob's photo and would be farthest from the camera on the right of the photo.