The Ankarana Massif consists of a limestone shelf which imposes a picturesque land-form on the few adventurers who find this remote forest. As the limestone has weathered over geologic time, this karst formation often exhibits spiry pinnacles, called "tsingy" locally. The name derives from the Malagasy word which means "walk on tiptoe", used by the earliest settlers from around 1500 years ago to describe the sharpness of the rugged limestone shelves. There are an abundance of limestone caves and virgin forests that shelter the diverse wildlife of the Ankarana region. In places the cave roofs have collapsed to form isolated forests and the vegetation of the gorges is also protected by the topography. Subterranean rivers provide a natural perennial irrigation system.