It's not widely known that Ailsa Craig, a prominent rock sticking out of the sea in the Firth of Clyde, played a prominent role in the early discoveries about the nature and extent of the Irish Sea Glacier. The rock type at Ailsa Craig is a peculiar microgranite, for the most part white in colour but with myriads of little blue specks visible to the naked eye. There is nothing quite like it, although I must admit to seeing many other "microgranite" types of erratics on the Pembrokeshire coast which could have come from North Wales or even Ireland. But small pebbles of Ailsa Craig rock are found on many of the beaches of North Pembrokeshire. I have found them at Poppit, Newport, Aberfforest, Aberrhigian, Aber-mawr and Aberbach. Wherever you find these pebbles, you know that there is Irish Sea till somewhere in the vicinity. Below is an early map made by WB Wright following his researches in the 1930's.
By the way, Ailsa Craig microgranite was (and still is?) the favoured rock used in the manufacture of curling stones........
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