So this could probably be it’s own thread, but I feel like we could totally talk more, as a group, about the significance of wells and depositional offerings

That may indeed be related! Does look like a preference for white stones.

So, it’s not exactly the same thing described here, but it might be related. Here’s a reference to a white stone or pebble having been ritually deposited into well in the Netherlands

https://collectie.huisvanhilde.nl/pdf/Pre-Christian-gods-and-animal%20symbolism-Van-Eerden-Nicolay.pdf