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ferruginous gases, &c., had been emitted. The action of these gases on the rocks had, amongst other transformations, produced laterite. The paper was written under the impression that the formation of plutonic rocks and plutonic action in sedimentary rocks were confined to deep subterranean levels (see the writings of Mr. Lyell and other English geologists). Hence it seemed necessary to believe that the superficial igneous action with which the paper was mainly concerned, was wholly unconnected with the granitic and other plutonic rocks of the district; subsequent investigation of some of the best developments of these led to the conviction that the Tartarean theory was inapplicable to them at least, The disturbed sedimentary rocks were re-examined free from the bias of that theory, and it then appeared, that, while the evidence in favour of the metamorphic origin of the laterites, &c., was so strong and varied that it might be now recorded as a demonstrated fact; there were no apparent obstacles to the reception of the simple hypothesis that they were caused by plutonic agency, and that the plutonic rocks of the districts were themselves the agents of the alteration or the effects of one and the same hypogene agency. This hypothesis embraces at once the whole region of elevation in which Singapore is situated, with all the plutonic, volcanic and metamorphic phenomena which it exhibits. It refers the whole to one cause operating throughout a long period of time, and which has not yet entirely ceased to operate, as the volcanic emissions of Sumatra and the vibrations of the whole region, from time to time, and the thermal springs of Sumatra and the Peninsula, constantly testify to us. This cause is the existence of an internal plutonic intumescence, or nucleus, which has slowly swollen up, fracturing the sedimentary strata, saturating and seaming them with its exhalations, and as it forced itself up beneath them and through the gorges and fissures, at once upheaving them and feeding on their substance, till, in many places, it pressed and eat through them to the refrigerating surface, and rose, congealing, into the air or sea. It is this latter circumstance that distinguishes the region from all those which have been observed by European geologists, and it is this singularly high level which the plutonic reduction has reached that explains the extraordinary appearances which the unreduced superficial rocks have so often assumed. The metamorphosed rocks of Europe evinced a deep subterranean saturation with plutonic exhalations, and European
geologists concluded that plutonic action was necessarily deeply subterraneous. But here, I think, we find a subaerial or subaqueous plutonic activity; and where the plutonic level has not reached that of the pre-existing rocks, a new kind of metamorphism appropriate to the new conditions under which the plutonic exhalations have operated.
The interest which the discussions respecting laterite have given to that rock, tends to invest it with undue importance geologically. The ferruginous emissions have affected all rocks indiscriminately, and their action on sandstones, grits and conglomerates is as well marked as that on clays, marls and shales, although the latter only produces proper laterite. Even in the clays, laterite denotes one only of many degrees and forms of alteration. To express the origin of these rocks and its unity, to record the cause of the difficulties which they have presented, and to distinguish them from true metamorphic rocks, I would propose, avoiding any new technical names, to term them simply the iron-masked rocks of the Indo-Australian regions. This term will include the principal or plutonically ferruginated rocks, which, without being either completely reduced or metamorphosed, have been either wholly disguised or partially altered by ferruginous emissions, which have saturated them in the mass-or only affected them in fissures and seams,or been interfused between portions of the rocks not actually separated by fissures, but intersected by planes of mere disconuity, the sides of which have an imperfect cohesion, or having a common border of inferior density and increased porosity caused either by interruptions in the original deposition of the matter of the rock or by unequal stretching or incipient cleavage. The term may be also extended, perhaps, to those sedimentary beds in which the iron saturation, although coeval with the deposit of the other constituents of the rock, has served to obscure or conceal their true nature as well as the derivation of the beds themselves. These beds appear to have been sometimes formed by superficial layers of gravel, &c. being permeated by iron solutions. With these must not be confounded the broad bands lying over and beside the heads of iron-masked dykes, and which, having been in a loose gravelly or fragmentary state at the time when the plutonic emissions passed through them, became cemented into hard, and occasionally scoreous, ferruginated conglomerates, &c. and are therefore proper plutonically iron-masked rocks.]
Before entering on a detailed account of the mineralogical features of Singapore, it will be convenient to bring into a preliminary paper some discussions of a theoretical nature, which, if not thus separated from the former, might, in the sequel, occasion frequent interruptions and some confusion. A brief sketch of the topography of the Island will suffice as a basis for the remarks which follow it.
The Island is of an irregular figure, when correctly laid down, (for the published maps, with the exception of Mr. Thomson's, are very incorrect,) resembling a bat, the head being at Tanjong Sinoko, in the old strait, the tail at Tullah Blanga, or rather Blakan Mati,—the western wing being fully expanded and the eastern a little retracted. Its greatest length from Pulo Campong or Point Macalister, on the west, to Tanjong Changai on the east, i. e. between the tips of the wings, is 21 miles. Its greatest breadth from T. Sinoko to T. Blangah coast, i. e. from the head to the tail, is 12 miles. Its superficial extent is roughly calculated at 200 square miles.
The town of Singapore, to start from the best known point, is situated at the south-western extremity of a flat alluvial tract, of which the greatest length in a straight line near the sea-beach is about 6 miles, and the greatest breadth inland about 27 miles. Three well marked deposits occur in this flat. A stiff clay of a greyish hue, becoming in some places darker and even blackish ; a whitish, greyish or yellowish sand; and a vegetable deposit, consisting, where most recent, of fragments of wood or masses of aquatic plants more or less decomposed, and, where older, of a soft peaty matter passing into a black mud. The mode in which these beds have been deposited will be described hereafter. The west side of this plain is marked by low rounded hillocks, separated by openings on the same level as the plain. On following these in a northwesterly direction, the former are found to be the extremities of distinct ranges of hills, and the latter the mouths of valleys between them, the principal extending about six miles inland. The largest valley, along which there is a public road, terminates a little to the south of a group of hills called Bukit Temah, the summit of which is 530 feet above the level of the sea, and the highest point in the Island. From this
group the valley and the stream which drains it borrow their name, The coast of Singapore to the S. W. of this valley also follows a N. W. direction. The intervening space is occupied towards the sea by a
prominent range of hills rising abruptly to a height of 300 feet at Tullah Blanga, which has lately been made the signal station. Towards the Bukit Temah valley a broad irregular range of hills is united apparently with the Tullah Blanga range on the N. W., and as it proceeds the S. E. separates from it and gives room for a broad swampy flat, from which the Singapore River flows. Nearer Town the range bifurcates, one of the forks terminating in Government Hill and the other in Mount Sophia. These Hills approach close to each other, but proceeding inland the two divisions of the range draw further back, and a secondary valley of considerable breadth, and about two miles in length, is formed. The range on the N. E. of Bukit Temah valley springs from Bukit Temah, and terminates in a low broad sandy elevation which slopes almost insensibly till it emerges in the plain. It is in some places about l} miles broad. The configuration of the range,—and most of the others have many features in common with it, may be partially observed in proceeding up the Bukit Temah valley. A succession of low hills present their rounded ends stretching into the valley which expands into the concave or sinuous hollows between them. The lateral valleys thus formed are of various figures and extent. Many resemble a horse shoe or amphitheatre. The upper extremities of most are of this shape, and similar indentations occur in the course of the more protracted, at the necks connecting the different hillocks which form their sides. When we strike across the range we are at first confused by the number of hillocks and hollows only partially cleared of jungle ; but under patient observation they gradually assume a certain order ; about the centre of the range the ground is a comparatively elevated and broad tract, but very irregular in its configuration. All these irregularities however, it is probable, have relation to the lateral ranges. These are seen to branch off to the north and south in a series of hillocks joined to each other by their sides and sometimes by an elongated neck. Towards the valley they often bifurcate, one limb sometimes taking a direction parallel to the range and then sweeping round and expanding into one of the broad hillocks whose ends approach the public road. The peculiar character of the topography of the country arises from the multitude and individual smallness of the hills, and the circumstance of the valleys which penetrate between the principal ranges and their branches, being, except towards the centres of the ranges, per
fectly flat, and very little above the level of the sea, so that the winding outlines of the bases of the hills are nearly as distinctly marked as if they sunk into the level sheet of a lake. We have in fact regular mountain ranges in miniature, and so symmetrical with all the apparent irregularity, that if the highest or summit lines of the ranges and their lateral members were correctly laid down on a map they would present no remote resemblance to the section of a tree. Beyond the last mentioned range another long valley occurs.* The stream Balastier which flows through it has its rise in Bukit Temah. The further or N. E. side of this valley is formed by the Kallang range of hills, the upper extremity of which is also connected with Bukit Temah : its lower division is penetrated by a long secondary valley. One of its summits rises considerably above the general level of the hills. Beyond it the valley of the Kallang river stretches inland. This valley has not been examined up to the top, but it is believed the river rises to the north of Bukit Temah in a continuation of that range. All the preceding ranges terminate in the plain or to the west of it and the Kallang, Balestier, Bukit Temah and Singapore rivers all cross the plain, converge towards the town, the three former uniting their waters, and flow through it. The next range beyond the Kallang valley is the central range or backbone of the eastern part of the Island. It does not terminate at the line where those already described sink into the plain, but continues its course to the eastward, sending out lateral ranges, the southern and western extremities of which form the boundaries of the plain. This range terminates at the Red cliffs. All the hills on the east and N. E. sides of the Island appear to be expansions of it. The valleys between the lateral ranges are bolder and deeper than those in the ranges first described, owing to the hills being generally higher and steeper. This range is connected with the Bukit Temah range. In its central parts it displays broad undulating tracts on a larger scale than the other ranges. Amongst the multitude of valleys which its branches include there is one on the northern side of some size in which the Serangoon stream rises. This valley seems to be a peaty swamp.
into a broad tract of mangrove jungle where the stream is lost in a creek which opens into the old straits of Singapore. Other streams fall into the straits
* For much information respecting these difficultly accessible valleys I am indebted 10 Mr, Thomson, the able and indefatigable Surveyor to Government for the Straits.