Are They Mixing Script?

Years ago, I was using 19th century congregational records of a Lutheran church in Illinois. Most members of the church were natives of Germany as was the pastor who wrote the records I was using. I was having difficulty reading the records until I realized that he was writing in English script for most of the record, but that he was slipping in a Germanic script for names, places of birth, and the occasional random word. The records were in English, but the non-English script made transcription an occasional problem.