Soapy Sam said:jj- The Ardnamurchan peninsula is the most westerly point of the British mainland, despite all the nonsense about Land's End. The photo shows basically a section through a triple intrusive centre, part of the N.Atlantic opening "Hebridean" volcanic province including Skye, Rum, Mull, The Antrim lavas in Ireland, and of course (somewhat later) Iceland.
Any caldera would have been a kilometre or several above the ground level in the photo. Great place. I spent 8 weeks there in 1976 mapping rocks and drinking beer.
I'll be looking at a map tonight. Glad I wasn't there when it was live