While we waited on the Bay of Fundy for a ferry to take us to Nova Scotia, we walked around on a little patch of shore. There were lots of sea-smoothened pieces of shale there, perfect for skipping on the waves, or for decorating a piece of driftwood.

You see the slightly sparkly stone, four from the right end? I have another piece like that. That's not shale. We thought it might be coal, but couldn't be sure.**
Later, we were staying in an old house in the coastal town of Port Hood. The house looked, from the exterior, like it ought to be haunted. We found out it had been built by someone who had made money in coal mining. Among the setbacks (disasters, more like) were that the mines sometimes flooded. Gradually, we realized that the mines had been . . . under the sea. As Wakanomori said: they would have found coal seams in the cliffs and then... worked their way down to under-the-water.
I mean, coal mining is always scary work, but PUTTING IT UNDER THE OCEAN makes it considerably more scary. As the housekeeper at the (potentially) haunted house put it, "I don't know how hungry I'd have to be to go down into that."
A cliff (not at the same place... but representative)

Then at one of the northernmost inhabited points on Cape Breton, we went on a little boat out to see puffins (and did see them! I hope I can do a whole post about that trip) and other pelagic birds, and the young captain (third-generation of tour-boat operators) was telling us more about erstwhile undersea mines, and meanwhile there were seals out on the rocks, watching us.... and swimming in the water and regarding us with just their heads peeking out...

... and now I think, there is a story out there about the dangers of the mines, and flooded mines, and selkies, and when I have it worked out, I'll share it with you.
**The day after the puffin tour, we found ourselves a town called Sydney Mines, a much-boarded-up town that no longer has any mines, but that does have a fossil museum and a room given over to artifacts from the mining days. There was some coal on display, and I was able to confirm that yes, the item I'd picked up on Nova Scotia's southern coast was indeed coal. Maybe if I sleep with it under my pillow, that selkie mining story will come to me faster.