During a short holiday to North Wales in Whit-week, 1910, I was investigating the igneous rocks to the south of Llanfairfechan, more particularly the intrusive greenstones of the Geological Survey map. Since the publication of this map, over fifty years ago, several districts within it have been investigated in greater detail, especially as to the volcanic rocks, but much remains to be done petrographically. One of these greenstones turned out to be of exceptional interest, being of a type of rock hitherto, I believe, unrecorded in North Wales, so another visit was made to it in August, 1912.