Complex sentence: The Tsaratanana Massif region at the north end of the island contains, at, the highest point on the island and, north of this, the Montagne d'Ambre (Ambohitra), which is of volcanic origin.
Split into simpler sentences: The Tsaratanana Massif region at the north end of the island contains, at, the highest point on the island. Further north is the Montagne d'Ambre (Ambohitra), which is of volcanic origin.