Im writing a non-fiction book about a gardener and her garden. The place is on a wetland and close to what french people call "The Betoire", a very special thing for the garden that exists in Normandie. It is very vital to the book, but I still cannot understand it completely. In english, its called the swallow hole, but theres not much information about it.
Do you know anything about it? Do you have a geologist friend that could help me?