There's a pretty uninteresting looking hill called Foel Tryfan near Caernarfon and at the top is a rock that clearly consists of beach pebbles stuck together.
In Victorian times this outcrop was the subject of intense arguments between those who said it was proof of Noah's flood and those who preferred a glacial theory of origin, suggesting that the glaciers had scooped up pebbles from the nearby beach and deposited them on the top of the hill.
Of course both were completely wrong because the rock is in fact very early Cambrian, but Charles Darwin visited the site and it was quite amazing to stand there looking at the outcrop and thinking how the actual famous Charles Darwin had stood in the exact same spot at the time when geology was just developing as a separate science.
And here's the big quarry that was just over the top of the hill. There would have been glorious views over towards Penrhyn Llŷn in one direction and Anglesey in the other, but as you can see, the weather was very grey and so we need to go back another time to take better photos.