Complex sentence: The boy's education was of the most desultory kind, the most successful part belonging to the years 1848 and 1849, when he and his parents went on a tour of Europe.
Split into simpler sentences: The boy's education was of the most desultory kind. Far the least useless portion of it belonged to the years 1848 and 1849, when he accompanied his parents on a tour on the continent of Europe.