Very circular, in fact. A Wild Mass Guessing concept occurs to me here. On Earth, the Caribbean Sea also has a sort of irregular circularity to it. Enough geological exploration has occurred here for science to be reasonably sure a massive meteorite, or perhaps a comet or small asteroid, impacted here, off the coast of what is now Mexico, in one of those events Rincewind gloomily recorded for posterity in The Science of Discworld. You know, the sort of thing that in a well-ordered Universe only ever happens in Outer Space, which as we know begins a few planets away at a nice safe distance where our telescopes can watch the fireworks.
This Snowball Event happened a billion or so years ago, apparently, but its mark can still be seen today - apparently the Caribbean can be viewed as one huge impact crater that eventually filled up with water.
Now on the Discworld there is the legend of the Fifth Elephant that fell off and owing to the strange gravitational field of Great A'Tuin, fell to earth again. What if the greater mass of the falling elephant created an impact crater which then filled with water? After all, Uberwald is not far Hubwards and the Dwarfs are still mining the bounty... but a World Elephant must logically impact over an area at least a fifth of the size of the entire Disc... what if only the smaller part of it is available for mining under Uberwald? The rest of it had to go somewhere....AgProv (talk) 11:43, 19 January 2013 (GMT)