Процитируем, от чего ж не...
Письмо 211 к Роне Беар: "I have, I suppose, constructed an imaginary time, but
kept my feet on my own mother-earth for place."
Или вот, № 165 To the Houghton Mifflin Co.
"'Middle-earth', by the way, is not a name of a never-never land without relation to the world we live in (like the Mercury of Eddison). It is just a use of Middle English middel-erde (or erthe), altered from Old English Middangeard: the name for the inhabited lands of Men 'between the seas'. And though I have not attempted to relate the shape of the mountains and land-masses to what geologists may say or surmise about the nearer past, imaginatively
this 'history' is supposed to take place in a period of the actual Old World of this planet."