Middle Earth (which is one continent on the world called Arda) didn’t evolve by natural geological processes, it was created by a god-like being (one of the Valar) called Aulë [1]. These beings would continue to personally shape and transform the world over its short history (a few thousand years), compared to the real world. I think it’s entirely reasonable for the features to look designed when in fact it is.

[1] http://tolkiengateway.net/wiki/Middle_Earth#History