else it would have an independent existence from the members of the culture, and be literally the soul of an ethnic group, made out of invisible culture-stuff, much like the consciousness-stuff that John Searle says our minds our made of.

As I understood Geertz, he wasn't talking about invisible culture-stuff, he was talking about tacit culture stuff. The tacit understanding is how people in a culture can make changes which are likely to be satisfactory to other members of the culture, and how members of a culture identify what fits.

If my theory is correct, it gets really complicated as a culture changes over long periods of time and as a result of contact with other cultures.