Complex sentence: The Montagne Noire, on the southern border of the department, derives its name from the forests on its northern slope, and some of its peaks are from 3000 to 3500 ft high.
Split into simpler sentences: The Montagne Noire, on the southern border of the department, derives its name from the forests on its northern slope. Some of its peaks are from 3000 to 3500 ft high.