One advantage of living on a once-glaciated, mountainous, sea-girt peninsula is the many places the Earth's bedrock is exposed in ice-carved valleys and sea cliffs. The Dingle Peninsula in southwest Ireland has been a haunt of geologists since the mid-nineteenth century.
Here is a pic of Clogher Head on the end of the peninsula, from yesterday's walk. These are the oldest rocks of the peninsula, about 425 million years, from a time not long after plants and animals first invaded the land.
In the cliffs are lava flows mixed with shallow marine and non-marine sediments. Volcanoes in Ireland!
Just one of many clues geologists use to reconstruct the past, in this case a time when a pre-Atlantic Ocean was being squeezed out of existence in the collision of continents that raised the ancestral Appalachian and Caledonian Mountains, now mere remnants of their former selves and sundered by a new ocean.
In the era just after the collision, I could have walked the relatively short distance from Ireland to New England.