Originally Posted by
FunkyDexter
I was interested in this so I looked into it a few years back. Here's what I found (supplemented by a quick perusal of Wikipedia while posting to refresh the memory):-
They're two separate legends that don't really knit together properly.
The sword in the stone myth is the earlier of the two and is probably inspired by Sigmund pulling Odin's sword from a tree to prove his lineage in the Sigurd tales. In it's earliest inceptions there's nothing to indicate it's Excalibur (it's just Uther's sword) but some of the later tales start to conflate the two.
The Lady of the Lake myth appears considerably later and does conflict with the former legend. Some later stories continue to conflate the two, some go back to imagining the sword in the stone as just Uther's sword and not Excalibur and some (notably Malory) just give both legends and never bother trying to explain the discrepancy.
It's interesting to map the growth of the Arthurian legends over time as they change quite considerably. There no Guinevere in the early tales, for example - she was added in the high medieval period when chivalry was de rigeur. The holy grail's also a latter addition and only starts to appear around the time of the crusades. From what I remember Lancelot's also a pretty late addition.
edit> BTW if anyone wants a really fun twist on the Arthurian legends, Bernard Cornwells is particularly amusing. He has Guinevere as a complete slut, Merlin as a charlatan, Lancelot as a total coward who just happened to hire the right bard to write about him and Arthur as a total wimp. All god fun.