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down from above. There are undoubtedly cases which, if taken by themselves, this explanation will satisfy. But when we seek to convert this hypothesis into a general rule we are at once met by numerous discordant appearances. Thus, of the extensive layers of rubble or gravel-like fragments beneath a thick bed of clay which, as before mentioned, are found on broad even summits of hills and ridges, there are many where the clay is too compact and aluminous or the rubble too fine, for the latter to have descended from the surface of the former, and where there are no adjacent higher levels from which the former could have been degraded and superimposed upon the latter. There are other allied cases too which simple atmospherical causes will not account for and which bring us to the next hypothesis—that of
4.-EARTHQUAKES. The instances alluded to are where the heads of the strata are not merely converted into rubble and bent in the line of slope, but where they are in zigzag, crooked, or sinuous lines ;-—where adjacent layers are differently and irregularly deflected out of their planes ; where the rubble is here in large pieces lying in the direction of the proper plane or of a regular curve from it, and there shattered into a confused mass of small fragments, sometimes much thicker and sometimes much thinner than the unaltered layer itself ;-or where fragments of one layer are intermixed with those of an adjacent one, detached pieces of a sandstone layer for instance imbeddled in a layer of clay above it, or portions of both layers confusedly mingled till all trace of their lines of demarcation is lost.
It is clear that no ordinary mechanical operations caused by atmospherical forces could have produced such results, and that violent convulsive movements of the earth have left these records. In the slight earthquakes felt at Penang in 1843 it was remarked that the residents on the hills described their effects differently from the residents on the plain, or in language more exaggerated. In Belmont-house, which is situated an the summit of a peaked hill rising freely out of the Pentland chain, the tremor was particularly strong. Upon general mechanical principles it is evident that the shocks will be most severely felt wherever the rocks acted on are freest. Through a dense homogeneous mass extending uniformly in all directions equable undulations and vibrations
may pass without disturbing the internal arrangement, because the motive force will meet with an equal resistance throughout. But where the mass acted on suddenly changes from a dense to a lighter rock, fractures and other internal disturbances will follow according to the intensity of the force, and where the mass of rocks is met externally by the rare elastic mass of the atmosphere, the resistance in that direction being removed per saltum, the general centrifugal tendency which will be impressed by the nether forces, even when their proper direction is more horizontal than vertical, will cause the upper rock to a certain depth to be fractured, loosened and expanded, the external fragments and particles being perhaps quite free and even projected. In this condition the whole superficial mass will readily yield to continuing vibratory action, and any or all of the phenomena above described may be the result. It is a further argument in favour of mechanical convulsions of considerable violence and irregularity, that although the general dip of the strata of Singapore be from westerly to easterly, cases are found of a hill resting on the same apparent base with an adjoining one where the general rule operates, having its strata inclined from east to west, and even in the same hill particular sides or outlying ridges or spurs, present deviations both in the direction and in the angle of the dip.
5.-VOLCANIC ACTION. Hitherto we have remarked no phenomena that may not be referred to the ordinary mechanical or chemical forces acting at the surface of the earth, or to critical mechanical disturbances. But I have now to notice a large and varied class of facts which require different forces to be introduced. These facts are so numerous, so constant in their occurrence over every part of the Island which is open to examination, and not less than elsewhere in those parts from which the observations of writers on the geology or mineralogy of Singapore have been drawn, that it is difficult to conceive through what fatality they have hitherto, for the most part, escaped notice or been passed over as unimportant. The most obvious of these facts are dykes and veins of igneous rocks, masses in situ and scattered fragments of rocks, such as sandstone, clays, shales, granite, &c, altered by the action of fire ; rocks in veins and joints often highly indurated, whereby sandstone has acquired sometimes a cellular structure, and at other times externally a honey-combed
appearance; congeries of curved, zigzag and radiating veins in sandstone, clays and shales, filled with crystallizations, and both from their own appearance and the alteration in the rock in which they are found showing chemical or electrical action of a volcanic nature; the presence of sulphur accompanying anthracite in shales denigrated and rendered fuliginous by fire; the slagsy appearance of many rocks and fragments which are often covered externally by a shining black, bluish-black, or dull iridescent varnish or glaze ; the scoreous appearance of others, many being mere cinders; the abundant presence of oxides of iron, and particularly their intensity in those places where the other evidences of igneous action are most marked, and their absence where these are entirely wanting. It is impossible to refer these facts and others of an analogous character, which will be mentioned in a future paper in the description of particular localities, to any but volcanic causes. The reddish, reddish-brown and reddish-black rocks which are found so abundantly have been noticed by Lieutenant Newbold, Colonel Low and others. The general name of laterite has been sometimes applied to them. Colonel Low uses the terms “iron clay,” “ iron stone” and “iron ore.” The red soils have been in like manner called laterite or iron soils. Both terms appear to be objectionable. Laterite is a particular species of ferruginous clay which indurates on exposure to the atmosphere like many other rocks : it ought to be restricted to the clay to which it was assigned by Dr. Hamilton, and not indiscriminately applied to every new rock strongly marked by oxides of iron. With respect to the term iron clay or clay iron stone, it has not yet been shown that any of the proper argillaceous iron ores, into the composition of which carbonic acid enters so largely, are found in Singapore. If there are any they have been disguised and changed by heat, decomposing into peroxides. The fact however is that these so called laterites and iron ores, externally as to colour and form differing little if at all, prove often on examination to be only fragments of the common stratified rocks, sometimes calcined, sometimes indurated, and sometimes partially fused by heat. We cannot therefore resort to a prevalence either of laterite or iron ores to explain the geology of the Island, and are by the rocks, which have been so designated, led back to volcanic causes.
Laterite.--Many of the clayey hills here appear to me to be decomposed sienite, come. times unaltered by supervening volcanic action, but generally purtaking in the metamor
Such a comparatively small portion of Singapore has yet in any way been laid bare, and of the accessible parts, with certain exceptions, so little is open to inspection save the mere surface, that had my examination of the most favourable localities of the latter been much more minute and careful than it has been, I should still have hesitated to combine the results into any general hypothesis. But as such an hypothesis has been forced upon me while following up my inquiries, and no facts have hitherto been noticed to which it is irreconcileable, I shall endeavour to explain it, leaving to future observations to build it into a theory, or reject it as a fancy. And as I shall proceed in subsequent papers to furnish detailed accounts of different localities, the reader will be enabled to draw his own conclusions.
The general direction of the elevatory force to which the hills or Singapore and the neighbouring Islands owe their origin, was from W. by S. to E. by N. since their dip is generally in or near that direction. Although the undulations or upheavings had this general tendency, the causes to which they were due must have been of a somewhat irregular
phism which the matter of most of the elevated land has suffered from that cause. May I venture to suggest that the hypothesis which is developed in this paper for Singapore might, if applied to the laterite of India, perhaps explain its origin, and, in doing so, to a certain extent also reconcile the conflicting opinions that have been maintained regarding it. All that I have read of the great laterite formations of the south of India, and which extend to the heart of Bengal, where they are described by Dr. Buchanan, leads to the conclusion that they do not consist of purely volcanic, sedimentary or decomposed matter, but what I have termed semi-volcanic. The same formation is found at Malacca and analogous deposits at Singapore, and both inseparably associated and evidently contemporaneous with altered rocks of the kind previously noticed. If we conceive an area with trap, granite, sandstone, shale, &c. exposed at the surface (in the atmosphere or in the zea) and partly decomposed or disintegrated, to be subjected to a peculiar species of minor volcanic action like that which is described in this paper (the distinctive phenomenon probably of one and the same geological epoch) the result would be that, with the occasional exception of matter ejected from no great depth, and some dykes and veins, the previous soft surface rocks would be merely altered or metamorphosed by heat and impregnated with iron, derived perhaps from the basaltic and other ferriferous rocks through which the discharged steam, gases, and water had passed in their ascent, Whether the action took place under or above the sea would be determined by the presence or absence of the ordinary marks of oceanic denudation.
When clays strongly ferruginous, and soft from saturation with water, are dried, the iron previously held in solution by the water is deposited between the particles and cements them into a hard compact rock. Hence the induration of laterite clays on exposure to the atmosphere.
nature, at one time producing a superficial effect, either uniform in its character, or small in degree, and at another time increasing in violence, and at particular points causing convulsive elevations of the rocks in the form of hills, frequently in undulating ridges and chains, the linear directions of which were, it may be, determined by a pre-imposed tendency to fracture, as will be noticed in the sequel. This force was apparently of a volcanic, or what, to distinguish it from concentrated well developed volcanic action, may be called a semi-volcanic nature, producing great heat at particular places, which sometimes merely indurated or calcined the softer strata and reddened the superjacent soil, but often in steam or gases, and occasionally in mud or semi-fused rock burst through them, or found a vent in fissures caused by ruptures during the process of elevation. When the heat was most intense, fused rocks or semi-fused fragments were cast up through these vents. As its intensity decreased fragments less altered and masses of clay and sand were ejected. The volcanic steam, gases, or fluids were charged with iron which left strong marks of its presence wherever these were most active, rendering most of the fused and semi-fused rocks, in dykes or ejected above the surface, highly ferruginous and impregnating all the softer adjacent rocks.
In some places the force, although of unusual violence, was at the surface chiefly mechanical, rending solid sandstones and tossing up and mingling the fragments with masses of soft clays and shales. Thus on some parts of government hill and the adjoining hill (Mt. Sophia) large angular blocks of solid sandstone, some from 600 to 800 cubic feet in bulk, are found at the surface and at various depths beneath it in a confused mass of clays and shales. In the same hills however there were also subsequently formed volcanic fissures, through which torrified rocks were ejected into the air and strewed over the surface so as in some places to form a thick bed over the disrupted sandstone, &c.
This extreme degree of local mechanical violence unaccompanied by simultaneous igneous action reaching the surface, is, however, rare, and may have been in some measure caused by a greater thickness and compactness in the resisting rock. But in general the upheaving of the hills has been attended with a violent agitation or tremor, producing the phenomena alluded to in a former page as due to concussion.
From what has been said it will be seen that the volcanic forces were