While reading A Tales of Two Cities by Charles Dickens, I noticed this sentence:
(Note: The sentence in the title of this question was shortened due to limited space.)
He wore an odd little sleek crisp flaxen wig, setting very close to his head: which wig, it is to be presumed, was made of ha...
This is probably okay in PDE, "I know Jack and Jane went out to lunch together: which restaurant is hard to say." -- (I made this one up.)
Wow, the top five hits of "relative determinative" are about another language!
> La relative déterminative est nécessaire au sens de la phrase.
> Maintenir dans l'écrit la différence entre subordonnée relative explicative et subordonnée relative déterminative (ou restrictive) est essentiel ...
> C'est "que Jeanne vous a donnée" qui est une relative "déterminative" car elle distingue l'information par rapport à une autre. Ce n'est pas ...
Oxford Modern English Grammar (Bas Aarts) has something about "relative determinatives" as well.
> 3.3.5 Relative and free relative determinatives
> The relative determinative which occurs before nouns in relative clauses (sections 3.2.2.3 and 7.3.3). It cannot occur as an independent element.
"It cannot occur as an independent element."
I found this question on the English Stack Exchange, which appears to be about the same structure. I don't think the answers there really explain the structure other than to say it's a way to remove ambiguity. — cbh8 mins ago