NEW LAND FORMED.
Besides the new land formed by the convulsions above described, the sea by a gradual recess in some parts produces the same effect. Many instances of this kind, of no considerable extent however have been observed within the memory of persons now living. But it would seem to me that that large tract of land called Pulo Point, forming the bay of the name, near to Silebar, with much of the adjacent country has thus been left by the withdrawing or thrown up by the motion of the sea. Perhaps the point may have been at first an island (from whence its appellation of Pulo) and the parts more inland gradually united to it.* Various circumstances tend to corroborate such an opinion, and to evince the probability that this was not an original portion of the main but new, half-formed land. All the swamps and marshy grounds that lie within the beach, and near the extremity there are little else, are known, in consequence of repeated surveys, to be lower than the level of high-water; the bank of sand alone preventing an inundation. The country is not only quite free from hills or inequalities of any kind, but has scarcely a visible slope. Silebar River, which empties itself into Pulo Bay, is totally unlike those in other parts of the island. The motion of its stream is hardly perceptible; it is never affected by floods; its course is marked out, not by banks covered with ancient and venerable woods but by rows of mangroves and other aquatics springing from the ooze, and perfectly regular. Some miles from the mouth it opens into a beautiful and extensive lake, diversified with small islands, flat, and verdant with rushes only. The point of Pulo is covered with the arau tree (casuarina) or bastard-pine, as some have called it, which never grows but in the seasand and rises fast.
(*Footnote. Since I formed this conjecture I have been told that such a tradition of no very ancient date prevails amongst the inhabitants.)
ENCROACHMENT OF THE SEA.
None such are found toward Sungei-Lamo and the rest of the shore northward of Marlborough Point, where, on the contrary, you perceive the effects of continual depredations by the ocean. The old forest trees are there yearly undermined and, falling, obstruct the traveller; whilst about Pulo the arau-trees are continually springing up faster than they can be cut down or otherwise destroyed. Nature will not readily be forced from her course. The last time I visited that part there was a beautiful rising grove of these trees, establishing a possession in their proper soil. The country, as well immediately here about as to a considerable distance inland, is an entire bed of sand without any mixture of clay or mould, which I know to have been in vain sought for many miles up the neighbouring rivers. To the northward of Padang there is a plain which has evidently been, in former times, a bay. Traces of a shelving beach are there distinguishable at the distance of one hundred and fifty yards from the present boundary of the sea.
But upon what hypothesis can it be accounted for that the sea should commit depredations on the northern coast, of which there are the most evident tokens as high up at least as Ipu, and probably to Indrapura, where the shelter of the neighbouring islands may put a stop to them, and that it should restore the land to the southward in the manner I have described? I am aware that according to the general motion of the tides from east to west this coast ought to receive a continual accession proportioned to the loss which others, exposed to the direction of this motion, must and do sustain; and it is likely that it does gain upon the whole. But the nature of my work obliges me to be more attentive to effects than causes, and to record facts though they should clash with systems the most just in theory, and most respectable in point of authority.
ISLANDS NEAR THE WEST COAST.
The chain of islands which lie parallel with the west coast of Sumatra may probably have once formed a part of the main and been separated from it, either by some violent effort of nature, or the gradual attrition of the sea. I should scarcely introduce the mention of this apparently vague surmise but that a circumstance presents itself on the coast which affords some stronger colour of proof than can be usually obtained in such instances. In many places, and particularly about Pally, we observe detached pieces of land standing singly, as islands, at the distance of one or two hundred yards from the shore, which were headlands of points running out into the sea within the remembrance of the inhabitants. The tops continue covered with trees or shrubs; but the sides are bare, abrupt, and perpendicular. The progress of insulation here is obvious and incontrovertible, and why may not larger islands, at a greater distance, have been formed in the revolution of ages by the same accidents? The probability is heightened by the direction of the islands Nias, Batu, Mantawei, Pagi, Mego, etc., the similarity of the rock, soil, and productions, and the regularity of soundings between them and the main, whilst without them the depth is unfathomable.
CORAL ROCKS.
Where the shore is flat or shelving the coast of Sumatra, as of all other tropical islands, is defended from the attacks of the sea by a reef or ledge of coral rock on which the surfs exert their violence without further effect than that of keeping its surface even, and reducing to powder those beautiful excrescences and ramifications which have been so much the object of the naturalist's curiosity, and which some ingenious men who have analysed them contend to be the work of insects. The coral powder is in particular places accumulated on the shore in great quantities, and appears, when not closely inspected, like a fine white sand.