Ger. "Sollen" VS Engl. "Shall"

Hello,
"Sollen" means "Shall" and they both are etymogically from the same
origin. But how is it that sh ----> s from english to german, I have
never heard of this transformation.
"Sollen" also gave "die Schuld" (the debt) in German, here we find
the "sch" we were waiting for!
Anybody would have an explanation?
Thanx