When scribes started using miniscule, they only used miniscule. it was its own alphabet.they wrote completely in lowercase letters.they also didn't space out their sentences much.parchment was expensive so they didn't want to waste space.
It wasn't until Charlemagne's time that scribes invented "mixed case": using capital letters to start paragraphs and mark proper nouns while using miniscule for everything else. Capital letters helped break up the wall of text so it was easier to read.