Complex sentence: While in New Orleans, he was caught in a sleety rain, and on the steamboat trip upriver, he had a severe cold; on November 13 he left Brierfield to return to New Orleans.
Split into simpler sentences: While in New Orleans, he was caught in a sleety rain. During the steamboat trip upriver, he had a severe cold; on November 13 Davis left Brierfield to return to New Orleans.