TypeError: can't make subclass of Class

Why can't a class be an instance of class Class and also inherit from
class Class in ruby?

Let's say I defined a singleton method on Class:

1.9.3p0 :032 > class Class
1.9.3p0 :033?> def Class.class_singleton
1.9.3p0 :034?> puts 'class singleton'
1.9.3p0 :035?> end
1.9.3p0 :036?> end

And I want to create a class that can inherit that singleton method:

1.9.3p0 :039 > class Q < Class
1.9.3p0 :040?> end
TypeError: can't make subclass of Class

How then could it be possible to access that singleton method without
directly calling it on Class? And why is inheriting from Class not
allowed?