German "Stein"

["Dr. Jamshid Ibrahim"]

The German word for stone ,,Stein" is used in German very widely in
combinations particularly with proper names like surnames, names of
streets....
1. The combination of some words like Bernstein is clear to me but I
can't understand a name like Einstein "one stone".
2. Germany is not that mountainous so why this overuse of "Stein"(
maybe particularly in the north?) Any historic explanation?