A few weeks ago, I shared some sand that my dad brought back from the Butt of Lewis. On that same trip, he and my mom went to visit the island of Barra, where her family originated from before emigrating to eastern Canada in the 1770s.
Halfway through their holiday, I received an excited text message from my dad: “Tell me – the whole island seems like grey granite, so where does the white sand come from? (In fact all the west side beaches are white sand.) Is it coral?”
Eager for a distraction from my work, I did a quick lit review. The consensus seems that indeed, the white sand on the beaches has almost nothing to do with the gneiss found on the rest of the island. In essence, it seems as though most of the original sand was bulldozed there by glaciers during the last ice age or brought there by meltwater as they retreated. Then over the course of the past few thousand years, shell fragments have accumulated and overwhelmed the native glacial sand, making up 7.5% to 82.9% of the total sand. This results in the beautiful white beaches that you see today (Jehu & Craig, 1924; Goodenough & Merritt, 2007).
This might be my favourite sample of sand that I have analyzed yet- it is incredibly shelly, and every photo reveals beautiful new shapes and patterns. I think I will just let the sand speak for itself:
I love the spiral shells. Last summer I read a really cool book about the evolution of mollusks and seashells: Spirals in Time: The Secret Life and Curious Afterlife of Seashells. Worth a read if you like this sort of thing!
I hope you enjoyed those as much as I did. I just wish I knew more about ecology so that I had a better idea of what we were actually seeing here!
Goodenough, K., & Merritt, J. (2007). The Outer Hebrides: a landscape fashioned by geology. Scottish Natural Heritage.
Jehu, T., & Craig, R. (1924). XXII.—Geology of the Outer Hebrides. Part I.—The Barra Isles. Transactions of the Royal Society of Edinburgh, 53(2), 419-441.