But the thinly-spread Indo-Javanese culture, in few places penetrating much below the surface, received a rude shock from the Muhammadan irruption, its natural development being almost everywhere arrested, or else either effaced or displaced by Islam. No trace can any longer be detected of graphic signs in Borneo, where the aborigines have retained the savage state even in those southern districts where Buddhism or Brahmanism had certainly been propagated long before the arrival of the Muhammadan Malays. But elsewhere the Javanese stock alphabet has shown extraordinary vitality, persisting under diverse forms down to the present day, not only amongst the semi-civilised Mussulman peoples, such as the Sumatran Rejangs[530], Korinchi, and Lampongs, the Bugis and Mangkassaras of Celebes, and the (now Christian) Tagalogs and Visayas of the Philippines, but even amongst the somewhat rude and pagan Palawan natives, the wild Manguianes of Mindoro, and the cannibal Battas[531] of North Sumatra. These Battas, however, despite their undoubted cannibalism[532], cannot be called savages, at least without some reserve. They are skilful stock-breeders and agriculturists, raising fine crops of maize and rice; they dwell together in large, settled communities with an organised government, hereditary chiefs, popular assemblies, and a written civil and penal code. There is even an effective postal system, which utilises for letter-boxes the hollow tree-trunks at all the cross-roads, and is largely patronised by the young men and women, all of whom read and write, and carry on an animated correspondence in their degraded Devanagari script, which is written on palm-leaves in vertical lines running upwards and from right to left. The Battas also excel in several industries, such as pottery, weaving, jewellery, iron work, and house-building, their picturesque dwellings, which resemble Swiss chalets, rising to two stories above the ground-floor reserved for the live stock. For these arts they are no doubt largely indebted to their Hindu teachers, from whom also they have inherited some of their religious ideas, such as the triune deity--Creator, Preserver, and Destroyer--besides other inferior divinities collectively called _diebata_, a modified form of the Indian _devate_[533].