There's a complete lack of logic in the supposition of a giant mountain creating night and day. Apart from the points Mundi has made, which even alone are enough to discredit this theory, if the sun were to travel around this mountain, we wouldn't have sunrise and sunset, instead, we'd see the sun begin to disapear behind the mountain, from side to side. And, of course, there'd have to be a mountain for it to disappear behind. There isn't.
Surely you can't honestly be supporting this theory, Dionysios, can you? Even if we look at this through a Christian doctrine point of view (as you seem to be doing by citing this "cosmologist"'s religion, which has otherwise no relevance to the subject) St. Augustine discouraged christians from "making statements about the physical world that were at odds with reason, since they would only bring our faith into contempt and disrepute."
And lastly, the fact that "practically all the most ancient religions and traditions throughout the world" mention this mountain means nothing. Ever heard of Carl Jung? You may want to look into his writings. It's a completely natural thing for humans to use mountains in their religions as mountains inspire wonder in us. Simply put, just because lots of people said something doesn't make it true, even if these people were spread out and didn't come into contact. All the most ancient religions were polytheist, does that mean there are many gods?