People who take a "marble cake" view of federalism believe that

In the marble cake, the layers are visible, but they also intermix in the border region and the borders are not clear. The Marble cake view is corresponding to the cooperative federalists, where the federal and state goverments cooperate rather than be very separate.

An informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.