Russel Wallace : Alfred Russell Wallace (sic)
Expedition to Central Sumatra' (S320: 1879)
From the general character of the distribution of the mountains, and the rivers, all flowing to the north-east, a very tolerable idea could be formed of the past physical history of the country. It was quite evident that the grand range of volcanic mountains was comparatively recent, and that the great bulk of the level portion of the island had been produced by the wearing away of the mountains and by the matter poured out by the volcanoes being carried down by the rivers into a shallow sea. Therefore, probably a few hundred thousand years ago Sumatra was very much smaller than at present, consisting of a great chain of mountains with a comparatively narrow border of land on each side. A very curious point in natural history showed that such was the case. The island of Banka was a totally distinct island from Sumatra, being granite, and was never joined to Sumatra, a wide arm of the sea having existed between the two. This was shown by the fact that in Banka there were animals, birds, and insects quite distinct from those of Sumatra. The fact had been ascertained by one of the Dutch residents in Banka, and instead of being a piece [[p. 777]] of Sumatra, this small island was really a piece of Malacca, having the same geological structure, and there could be no doubt that it was once joined to the peninsula of Malacca. Before the volcanoes originated, however, Sumatra must also have been joined to Malacca, the continent of Asia being extended so as to include Sumatra and the small islands beyond. The row of islands on the west coast also contained some peculiar animals, and were connected with Sumatra by a shallow sea, whereas immediately outside them the sea sank suddenly to the enormous depths of the Indian Ocean; and the wonderful similarity on the whole of the animals of Sumatra with those of the Malay Peninsula rendered it perfectly certain that the two countries were at one time joined, and at a not very remote period. Still it was remote enough for the intervening land to have sunk down, and then for the volcanoes to have arisen and poured such a mass of matter into the water as to form the enormous expanse of undulating country, which was largely formed of a red clayey substance such as was seen in almost all regions where volcanoes abound. It had been deposited in the sea, then uplifted, and then cut through by the rivers.
As the mountains were approached, the variety and beauty of the vegetation increased, and all the more remarkable birds and insects were found there, as well as the higher races of Malays. The whole of the southern portion of Sumatra was inhabited by a genuine Malay race; in fact, they were the originals of the Malays, speaking various dialects of the Malay language. Further north there were other races, which, though belonging to the Malay type, were not of the true Malay stock, and spoke different languages. No doubt, all these matters would be clearly explained in the work which Professor Veth had promised, and of which he supposed that the beautiful photographs now exhibited would form the illustrations.
1. Since making this observation I have met with a paper (in the 'Geological Magazine,' 1877), on the Geology of Sumatra, by M. R. D. M. Verbeek, the Director of the Geological Survey of the West Coast of Sumatra, in which it is stated that the Ombilin coal-field of the Padang Highlands consists of sandstones nearly 1000 feet thick, without recognisable organic remains, but resting unconformably on a marl-shale formation which is considered to be of Eocene age or intermediate between the Eocene and Cretaceous formations. The coal of Sumatra will therefore belong to the Tertiary period; and as it now forms the summits of high mountains on the central plateau, it affords an indication of the comparatively modern origin of the great mountain range of the island. [[on p. 776]]