If you are talking about how the bottom is rounded my guess is like the old Charnley Forest stones. This is because they were moulded by a driver blade. Also the labeled Glanrafon interestingly were sold as another sort of Charnley Forest stone even though they are a type of Welsh slate. Maybe it is a Glanrafon can only tell really by feel.Interesting. This fiddich does have backside cut reminiscent of several charns I have from when they all went into blocks of wood it seemed.
You have some nice stones there for sure! Appreciate all the info.