Good question, Don Firth (18 Jul 15 - 06:40 PM). As pointed out by previous posters, the immediate source was Hendrik Willem van Loon's History of Mankind (1922):

High in the North in a land called Svithjod there is a mountain. It is a hundred miles long and a hundred miles high and once every thousand years a little bird comes to this mountain to sharpen its beak. When the mountain has thus been worn away a single day of eternity will have passed.

The Grimms' Pomerania is replaced by Svithjod (Svíþjóð) = Sweden, a country which had annexed Pomerania in the 17th century. The gist is "a land far away, but known by the intended readers to exist for real" (- American children may have associated Pomerania with dogs).

In the YouTube linked by GUEST,kassy61 (08 Jun 09 - 07:54 PM), the name of the songwriter is mentioned, who seems to be responsible for the skyward transposition of the scene, thus the real sinner.