Complex sentence: Rosecrans had a voracious appetite for conversation, especially when he was unable to sleep; in Garfield, he found "the first well read person in the Army" and the ideal candidate for discussions that ran deep into the night.
Split into simpler sentences: Rosecrans had a voracious appetite for conversation, especially when he was unable to sleep. In Garfield, he found "the first well read person in the Army" and the ideal candidate for discussions that ran deep into the night.