金石 きんせき併用 へいよう時代 じだいでしょう
kinsekie iyōjidaideshō

Noun
Desu Copula

Expresses probability in a polite manner ("probably…") of 金石併用時代

1. Probably an age of metal and stone.; Likely a time when metal and stone were used together.

Polite
Presumptive
Conjecture