"But on Earth and on other planets of the pocket universes, the hills, mountains, valleys, plains, the rivers, lakes, and seas, seldom altered." (The Lavalite World" by Philip José Farmer)
Sounds like they are on a world with an evershifting landscape. Given that the book is called the Lavalite World it brings images of clumps of matter shifting, breaking off, and merging back with each other just like a lava lamp.
Here's how Third Sentence Thursday works:
1) Take the book you are reading now and post the third sentence
2) Review this sentence anyway you want (funny and silly reviews encouraged)
3) Post a link to your sentence to Sniffly Kitty's Third Sentence Post for this week.