Caedmon's Hymn--a hypothesis
Having reviewed all the old texts and all the translations I can find, it seems to me that the history of the dissemination of this hymn reveals both they typical path of mishearing and misunderstanding that any oral text will suffer (without that I can see any overt attempt to bend it to a new purpose) as well as, in this particular case, an attempt to reconstruct a meaning as effect of Caedmon's particularly odd use of "Midden-geard." In brief, my guess is that the poem was, in the original, must simpler than later rehearsings imagined. The structural paraphrase would be: Time to praise God almighty who made for men first heaven for a roof, then the middle area, and then the firm ground. But since "midden-geard" was generally understood as the earth, as the "firnum folden" between Heaven/sky and Hell/underground, Cademon's use of the term for the stuff between the ground and the roof was baffling. And this is what led to all sorts of variations...