References in classic literature ?
It was of about the same diameter as the entrance at the foot of the tree, and opened directly upon a large flat limb, the well worn surface of which testified to its long continued use as an avenue for some creature to and from this remarkable shaft.
I am Big Foot, Little Brother, and thou art Little Foot, the Gond.
The most common shell is a massive gigantic oyster, sometimes even a foot in diameter.