A glass coracle, the source of all things, like an egg. The round imagery could be taken to its extremes, reading The Poetics of Space by Gaston Bachelard, roundness is a phenomenon:

''Life is probably round'' Van Gogh
''He had been told that life was beautiful. No! Life is round'' Joe Bousquet
''A walnut makes me quite round'' La Fontain

Coracles are commonly compared to nuts or shells, which sits in direct contrast to the fragility of the actual boat.