I agree with the other comments. But why is it that we can't say "the Mount Everest"? I think it is because there is no noun there for "the" to modify. When you say "the Atlantic Ocean", "the" goes with the noun "ocean". When you say "the Rocky Mountains", "the" goes with "mountains". But when you say "the Mount Everest", "the" could only modify "mount" and "Everest" would just be dangling there. I do believe you could say, although nobody does actually say it, "the Everest Mountain". That's good English, even though nobody has ever said it.