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At the southern extremity of the western St. John's (Púlo Sikijang) two adjoining hills have been formed by strata being bent into a convex shape-rising only a few feet above the level of the beach. There is a remarkable approach to uniformity in the strike of all the strata and in the direction of the hill ranges. Speaking generally, it may be said to approximate to N. W.-S. E. The hills have commonly mamillary surfaces. The ranges may be said to consist of distinct hills bulging out and united at their sides. The central hills are generally the more bulky. Lateral hills ramify on each side to a short distance. The whole connected system is disposed in a symmetrical ramose manner, indicating a wonderful uniformity in the mode of operation of the dynamical forces which produced them. The investigation of the forms of these hills, and of the laws of the mechanical forces of which they are the result, assumes a high interest and importance when we find that these forms are not confined to Singapore, but are repeated in low hill ranges over large portions of the Peninsula, Sumatra, Southern India, Northern India, Northern Australia, &c., and accompanied, as I believe, by volcanic phenomena of exactly the same nature as those which I have described. I do not say that the phenomena are identical at all points. In Singapore itself they vary almost infinitely. But they are always analogous, frequently the same, and, to my mind, are undoubtedly the product of one well marked species of volcanic* action.
I should not omit to notice the frequent occurrence, in those ranges which have been most burnt, of mounds or monticules of scoreous blocks, sometimes on the summits, and sometimes bulging out from the sides of hills. The ridges and angles of hills appear frequently to present scoreous blocks.
The valleys between the long hill ranges are, in Singapore, perfectly flat, so that they display the outlines of the bases of the ranges almost as well as if they still remained what they were at no very remote
* In reference to the igneous changes which the rocks have undergone, I use the words volcanic and plutonic indiscriminately, because a minute examination of some of the best marked developments of crystalline rocks (graduating from basaltic to granitic types) at the extremity of the Peninsula, has led me to think that though the distinction is useful and appropriate in some regions, the theory which it expresses is not sound as a general one-at least as expounded by many Geologists.
period, long narrow inlets of the sea. This circumstance also is not confined to Singapore.
I will now briefly notice the nature of the sedimentary rocks which have been more or less altered and elevated in the modes I have mentioned. If you think it worth while, you can, I dare say, procure a copy of Mr. Thomson's Chart of Singapore straits from the Admiralty for reference. It would scarcely be advisable at present to attempt to make a geological map. The southern portion of the Island (including the town, the adjacent district to the N. W; the ranges between the road from the town to Bukit Timah, the central and highest hill, and the sea to the S. W.), and the Islands of Blakan Mátí, Púlo Brání, St. Johns, &c., are compossd of shales, clays, sandstones and conglomerates, the shales predominating. It is impossible to refer these rocks to any place in your European systems, as no organic remains have yet been discovered, and the only rocks with which they are associated are hypogene. In their general appearance and mineralogical characters they agree with the aluminous and arenaceous beds of the new red sandstone. Between the parallel of strike passing through the town and the steep Tulloh Blangan range, there is an area about a mile in breadth, stretching from the sea inland over the Tanjong Pagar and Tanghir districts, and of course in a direction approaching to N. W., and in the opposite direction, including Pulo Brání and the eastern portion of Blakan Mátí, composed in great measure of shale strata, although a few of sandstone also occur. The prevailing colours of the shale beds are dull violet, liver brown and chocolate. Beds of the most lively variegated colours sometimes occur motled, striped, damasked, &c, the colours are white, yellow, orange, red, violet, purple, green, bluish and blackish, in addition to the dull violet and chocolate. To the N. E. of this tract sandstone is more frequently interstratified. To the S. W. sandstones, grits, and coarse conglomerates prevail ; and these are continued, interstratified however with some shales, from the range along the coast of Tulloh Blangan through the western portion of Blakan Mátí, and through Sikúkúr and Sikijáng (St. Johns), in a S. Westerly zone. I have not yet pursued this zone further across the strait, but the Island of Sámbo, on the other side, is a continuation of the same parallel of elevation, and may consist of the same rocks. To the N. E. of the town, a large alluvial plain sweeps into the country. The hills around it are principally arenaceous. The arenaceous band however on the N. W. of the plain merely skirts it. Beyond this band (and succeeding the sandstone ranges to the N. E. of the shale tract first noticed) a broad zone of clayey hills, of which the boundaries are irregular, but which may be from 3 to 4 miles in breadth, stretches through the heart of the Island to Búkit Timah, and thence across to the Sálát Támbroh or old strait of Singapore behind the Island. The tract to the S. W. of this, stretching from the parallel of the S. W. boundary of the shale band to the S. W. point of the Island (Tanjong Gúl), is composed principally of sandstone and shale, but granitic bases and ranges also occur. The great clay tract I believe to consist in large measure of decomposed hypogene rocks,-sienitic and granitic chiefly, (it has only however been partially examined or laid open). Blocks of these rocks are seen at the surface in some of the hills, and the sections made by roads so exactly resemble decomposed crystalline rocks that I have no doubt that the whole of the clay hills are at bottom hypogene rocks. Their structure and composition I believe to be very variable. This tract is continued over a considerable part of the rest of the Island to the N. E., but a large tract of sandstone (accompanied by a very little shale) stretches into it. The coast boundary of this tract is a line of about 4 miles, extending along the south eastern shore of the Island from Siglap to beyond Tánáh Merá Besár (the Red cliffs). It insulates the granitic N. E. projecting portion of the Island at Changy, embraces the northern coast from the inner extremity of this promontory to the inner extremity of that of Púngal, and then proceeds inland. The line of its junction on the N. W. with the granitic tract that surrounds it I have not yet ascertained, but it is probably irregular. On the S. W. it connects itself with the arenaceous band surrounding the plain previously mentioned, and, indeed, forms the larger portion of the boundary of the plain. then stretches inland for some distance, having the S. E. projection of the great granite tract interposed between it and the arenaceous and shaley bands, first above noticed. P. Ubin is entirely hypogene, varying from granitic to compact types. Hornblende is largely developed. The structure of the rocks is highly curious and interesting. I have given much attention to this Island, and in the beginning of September last sent a full account of it, and of the geological views to which it seemed to lead, to the Bataviaash Genootschap van Kunsten en Wetenschappen, in whose Transactions, the President writes me, it will appear. In this paper I had been led to some views with which I find Mr. Darwin had been occupied, and which are developed in the chapter on plutonic and metamorphic rocks in his geological observations on South America, of which, though bearing the same date as my paper, I did not receive a copy till about a fortnight ago. The germ of his ideas is however contained in his Volcanic Islands, which I have referred to in my paper. As I have also considered the subject from some other, and, as I believe, new points of view, I shall send you a copy of the paper in English, the Batavian Transactions being in Dutch.* The coast of the mainland behind P. Ubin consists of rocks some of which would be called plutonic and others volcanic like those of Púlo Ubin, but the whole are undoubtedly of the same contemporaneous origin. At Runto, in the estuary of the Johore River, sandstone, similar to that of the Singapore Red cliffs, and, like it, remarkable for being nearly horizontal, is exposed. Further up the River the rocks exposed are of a decomposed felspathic character, and exactly resemble some of those of the hypogene tract of Singapore. At one place a hard ferruginous crust about 9 inches thick overlaid a decomposed felspathic rock. Pulo Tikóng, Besar and Kechil, consist chiefly of sandstones and in part of shales, often greatly altered by volcanic action. On the coast to the S. E. near Johore Hill, or at Tanjong Pingrang, are found, within a small compass, soft shale or clay,-clay indurated so as to resemble, or become, chert,-conglomerate highly indurated and partially transformed,-quartz rock,--and traces of blackish brown slags,indicating various degrees, and even some difference in the mode of the volcanic action.
The connection between the crystalline and sedimentary rocks of the district is susceptible of two explanations. We may either consider the former in their fluid or viscous state as having been the immediate agents of the volcanic and mechanical forces to which the latter have been subjected, or we may consider the former as the product of the first plutonic action beneath this region; the latter as sedimentary rocks subsequently accumulated Cover them) during a period of quiescence, and their fracture, upheaval, and alteration as the effects of a new excitement to activity in the plutonic sea below, in which the old plutonic crust, with its sedimentary covering, was broken and upheaved, and ferruginous or ferro-siliceous gases copiously emitted through the lines of fracture. On either supposition the ferruginons character of the emissions would be accounted for, because the upper granites, &c. contain much iron in their hornblende, and whether the mass below the granite crust, had remained in its fluid state during the deposit of the sedimentary rocks, or had been wholly solidified and subsequently melted down
* In a general descriptive sketch of some portion of the Straits of Malacca which I sent to the Geographical Society some time ago, I mentioned the singular grooved rocks at the Chinese Quarries on P. U'bin, and hazarded some conjectures respecting their origin-when I wrote that paper I had made only one flying visit to the Quarries and was under the impression that the deep channels were confined to this locality. My first geological visit subsequently at once undeceived me. In the paper forwarded to the Batavian Society, I have shewn how these channels have resulted from the original structure of the rock under ordinary decomposing and eroding influences.
the gases given off from it, when rents were formed, would probably preserve the same character as those given off from its original surface before any granitic crust had been formed. I cannot stop now to explain how the prevailing plutonic theories, as applied to the phenomena of the district, seemed, at the time when the paper first mentioned was written, to require the adoption of the opinion that the granites, &c. were in existence when the volcanic action took place. Even under the influence of these theories I considered the point as very doubtful, and, although it involved consequences irreconcileable with these theories, I ventured to hazard the conjecture that the upper hypogene rocks had been the immediate agents of the changes. The examination of Pulo U’bin shook my faith in these theories as expounded by some of their principal advocates, and the conjecture assumed a high degree of probability. Latterly I had all but embraced it, but still suspended its complete adoption in the hope that I would discover some phenomenon amounting to ocular proof of its truth.
I have only another point to advert to before I come to Valacca. If you have taken any interest in Indian Geology, you are doubtless acquainted with the rock called laterite which prevails so largely in southern India, and is also found in Bengal, &c., and which, to this day, remains the most fertile subject of discord arnongst Indian Geologists, although the general opinion appears of late to have settled down in favor of its being a sedimentary deposit. In the paper first alluded to in