The Rocks of Paulo Ubin
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ROCKS OF PULO UBIN Rhee it
James Dichardson fogan.
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NATIONAL LIBRARY, ) B JULI9Y7
1159459
ma SSa.oFS1S | Log
OF PUELGO OBE H,
WITH SOME REMARKS ON THE FORMATION AND STRUCTURE OF HYPOGENE ROCKS AND ON THE METAMORPHIC THEORY.
Puic Ubin is an Island lying im the strait between Singapore and the coast of the Malayan Peninsula, of which the eastern extremity faces the entrance of the Johore river. It is about five miles in length, with a general direction from E. by SE. to W. by NW., and has a varying breadth from a mile to % of a mile. :
In detailing the results of four or five visits which I have made to it within the last few months, I shall first endeavour to convey some conception of the distinctive aspect of the Island, or that which would strike a stranger; and this object will be best served by giving my own first impressions as they were written down at the time in my Journal, even although they embrace some ideas that were afterwards corrected by a wider Survey. I shall next deseribe the rocks of the Island, so for os I have observed them, noticing slightly the scenery where it is most remarkable for its beauty. The concluding portion of the paper will be occupied with some deductions from the preceding details, a notice of the relations between the Island and the adjacent localities ond some remarks upon its bea- ring om geological theories current at present
To begin then with the impressions made by the first sight of the Island. I crossed from, a small Malayan campong on the coast of Singapore opposite Pulo Ubin, called Passier Ries. There is here a deep indentation in the Simgapore coost, or rather two hilly and wooded points (Tan- jong Changy and Tanjong Pongal), advance from it towards each extremity of P. (bin and in- elude with its southern shore a noble sheet of water about three miles long and two miles broad save at ils extremities, where it is contracted between the Points and P. Uiin to straits of about one mile in breadth. This Island-fronted Bay must originally have been much greater on the Singapore side, as the creck of Sirangoon’ winds (hrough a broad expanse of mangrove jungle, and terminates in a swampy valley the whole of which has heen accumulated on the old sea bed (1). As we left Passier Aves, the Strait, land locked on all sides and smooth on ils
Cl) What follows as far on p. 7 was copied from my Journal in o paper, chiefly relating to Piearg, which I aeotio the Royal Geographical Society of Looden in June last. 29" nem, 1647, A.
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surface, appeared like a lake amongst low hills, It is seemingly quite surrounded by jun- gic, the mangrove predominating wherever there has originally been a deep indentation in the shore, On the north the opposite side of the Old Strait of Singapore (Salat Tam- broh) is completely, etcluded from yview,,tave at.ope point,by P. Ubin, which shews likea densely wooded low hilly range. A broad bay on its shore is nearly filled by a low flat island or mud bank, called Pulo Tam (properly Kram); which is covered by a thick sheet of green gleaming mangroves. We stood across: the strait towards this Island, passed its eas- tern extremity, and then proceeded castward-along the shore of Pulo Uhin. Several rocky points slightly project from it, and+these are covered with trees of no great size, but which, from their not being so densely crowded as tropical jungles generally are, junite luxuriance with grace and [freedom of growth. The abundance and abruptness of the rocky masses Which are partially visible, clothed with mosses and lichens and with shrubs rooted in their clefis, prevent the trees from approximating, raise their trunks here and there into view, and, by limiling their number as in an artificial wood, afford space cnough above for the branches to expand into full-leaved wide-spreading canopies, om the dark and cool shadows of which the eye, dazzled by the radiance of the sea) wishfully lingers. The rocks are however less scen themselves than by these their effects, for such is the profusion of shrubs, un- derwood, creepers, and parasitce of various sorts, that the dead mincral masses seem to be imbued wilh botanic fecundity and wrapped in a living garment woven out of their own breasts, The little bays between the Points are nearly obliterated by level sheets of mangrove which, by their growth externally, tend constantly to convert the original irregular, into a straight, coast line.
One of the most striking features of the lake like scenery of the strait between Pulo [hin and the Singapore shore is Gumong Baw a broad pyramidal hill, which, as we approached the eastern extremity of Pulo Ubin, and the wide estuary ‘of Johore river on the left or north east and the wider mouth of the old Singapore strait on the right or south east gradually opened ,—was seen up the former at a distance of & or 6 miles. Although termed hy seamen Little Johore hill, it is, in reality, higher than Marbukit-or Johore hill which forms one of the moat prominent landmarks on entering the straits of Singapore from the China sea, From the regularity of its cone, which from this point of view seems to descend with almost per- fect evenness on all sides to a level a little above that of the sea, and its apparent isolation, it resembles a voleamie bill.
We stood across the strait between Pulo Uhin and P. Tikang to the small islets called P. Sgahat. On our return we pulled close in to one of the points on the south side of Pulo Ubin, where there are several Chinese quarrymen engaged in splitting granite for the supply of the builders in town. We were struck by the extraordinary appearance of some of the granite rocks on the beach. Their sides were grooved or fluted, presenting regular vertical furrows and ridges. A little way in from the beach, and on the lower face of a hill, stood a very large rock of which two faces were visible, the remainder being concealed by loxuriant jungle, and the summit overluog with shrubs and trailing plants. At a little distance it was hardly possible not to take it for a portion of an ancient temple rudely sculpfured out of the solid rock, since from ils front stood out what seemed to he a range of colossal misshapen images. On aseending to it through the brusliwood my amaze-
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ment increased, for while it was too irregular to be a work of art, it seamed to be too close an imitation of one for a natural production. Amidst the jungles of the granitic mountains of Pinang I had been familiar with all the shapes and positions which I had considered detached masses of that rock capable of assuming. I had there seen it in solid boulder-like blocks of vast size, sometimes cubical, and sometimes approximating to globus lar. 1 had also seen it in smaller blocks piled one over another with all the regularity of druidical masonry. But T had never ecen or read of granite carved by nature alter the fashion of the mass before which I stood. In the perpendicular face of the rock were scooped out, from top to bottom, deep concave hollows or grooves varying in breadth and depth. Between these the rock projected in huge unshapely columns like a row of rade idols. Towards the top these pillars were rounded. In some a slight curved groove or fissure cros sed ihe upper part, the convezity being downwards, and thus converting: the summit into a globe resting in o cup. Below the line of the fissure the pillar contracted very much on both sides as if it had been at this place scooped evenly out. It then bulged out on both sides, but much more on the left than the right. The sides next converged, and, lower down, approached more rapidly. They then bulged out again fill the soil hid the rock from further view. In some of the columns the curvesof the sidesassamed the form of a vase. The bot- toms of most of the hollows or channels between were nearly uniform in depth altho’ somewhat nneven of conchoidal, Of these singularly shaped columns five or six lad o close resemblance to each other, When viewed from the side they were all seen to be scooped quite round at the places where in the front view they contracted, #0 that their edges appeared thus (fig. 1.)
In fig. 2, a, @, is the lost of these pillars. Beyond it to the right the regularity is broken, and the grooves appear os in the shaded portions of the fig. The groove on the right of a, a, marked ¢, ¢, is a remarkable one, The upper part has a regular semi-cylin- drical shape. At the line b, b, it abrupily, bot with all the regularity of art, slopes inwards at a sharp angle, #o that the part darkly shaded forms a cavity apparently about five feet in depth. A slight groove, an inch or two in depth, is shewn at d, and deeper grooves appear further along. The pillars whose side view is as in fig. 1] are on the other side or to the left of a, a. Ascending the hill I managed to clamber to the top of the rock, where I found the grooves to be partially prolonged on the surface in an inclined direction, The surface al some places was hollowed -into cup like depressions. Climbing fur- ther up the hill T came, at no great distance, to another rock of much larger dimensions. It was reft or traversed by a chasm from 6 to & feet broad. The sides of the chasm were much fresher than the external surface, and the mass had evidently been split across at a time subsequent to its existence as a separate rock and the formation of the grooves with which it also was traversed in front. The extremity of one of the two masses projected for some dis- tance over the sloping ground so as to form a capacious cave. AL another side a larger frag- ment had fallen from the rock and lay against it. On its surface was a cup or rather spoon- shaped cavily about two feet in diameter and one in depth. At another place a second pro- jecting rock occured forming another cave, about thirteen paces in length. The entire length of the rock which thus projected seemed to be about forty paces. On the same side there were numerous grooves, some not exceeding a few inches in depth and breadth, others above
2! feet deep and about 3 feet broad. One groove I observed about six feet deep and two feet broad with small secondary or inner grooves fluting its surface. While examining this rock a heavy shower of rain began to fall, and as my time was exhausted [ was obliged to leave before 1 could make mote precise observations or any measurements, and, in trath, before I had recovered from my first sensation of wonder. It appeared to me that the rock must have been split on being elevated from a lower level, On returning I observed many smaller rocks near the beach with channeled sides. On the top of one of these there was a long ‘deep trough with small grooves converging into ils upper end, like the ribs of a fan, The rest of the surface was covered with slight depressions.
L believe this is the first time that grooved rocks have been observed so close upon the Equator. Their absence has been considered an argument im favour of the glacial theory of the boulder formation. None of the channels or grooves, however, which I observed resem- ble the parallel inclined or approximately horizontal forrows which are caused by the mo- tion of glaciers im descending the rocky trough of ao valley. But they appear to correspond strikingly, save in being vertical, with the giant cauldrons, passing into long deep grooves, which are described by Acasstz as being produced in the Alps and Jura by streams of water falling over the sides of chasms im advancing glaciers, and acting as a locomotive erosive force upon the subjacent rocks, My hurried and restricted observations hardly [warrant a conjecture as to the probable origin of the Pulo Ubin grooves. The idea that occurred to me on the spot was, that the several rocks, before they were shattered and separated by the force which placed them in their present posilions, and in some different local distribution of land and sea from that which now prevails, had formed the site of a cascade of no great force which had gradually worn the sides of the rocks into channels, A succession of falls would account for the relative positions of the rocks with respect to each other and for the spoon shaped hollows on the surfaces of some of them. It appeared to me that ordinary meteoric erosion ond decomposition were tolally inadequate to explain the shapes and size of the grooves. In many places they are overgrown with mosses, and in some, if mot im all, they are prolonged beneath the ground, and thus protected by the soil of the hill, which must haye covered them for a considerable period, since large trees are rooted in it. The aspect of the rocks is mot such as rapidly disintegrating granite wears, but, on the contrary, re- sembles that of an ancient building. L could find no trace of any fissures coinciding with the dircetion of the furrows. Yet there can be little doubt that, to whatever agency they may be referred, the grooves were first opened along lines where the cohesion of the granite was comparatively weak, The regularity with which the projecting columns of the rock first noticed are scooped round at two places across the direction of the grooves, scems to prove that the granite has an internal arrangement similar to that so frequently observed in this rock, and which causes it to be shattered into blocks more or less cubical. In one of the lower rocks which the Chinese are quarrying we found two parallel verlical veins traversing the eniire rock so as to include between them a plate about an inch in thickness. One side of this plate sparkled with metallic grains of a golden hue (iron pyrites). The other was covered with a rusty stain resulting probably from the fissure on that side having been per- meable by the air and the consequent decomposition of the grains.
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As we pulled away from this place and looked back, even the want of light and shade and the heavy rain that was falling did not prevent our acknowledging that it possessed o character of picturesque beauty of a very pleasing and uncommon kind. It, in trath, united the luxuriance and gracefulness of tropical vegetation with the open and irregular aspect of a wood on some river's bank, half rocky, in England. The jungle trees of Singa~ pore do not in general attain sufficient size to assume that air of grandeur which distin- guishes those on the Pinang mountains, and they are so blended with the underwood, which grows up like a thick crop of rank weeds between them, and so inferwoven by creeping and pendent plante into a dense mass of green, that their individuality is extinguished. The display of botanic life is wonderful in its measureless, all pervading etuberance, and this very profusion ministers to a deeper sense of the silent, soft, epirit-like, but mest po- tent and most motley, power of vegetation. Still no tree or humbler plant invites us to dwell delightedly on its own perfection. At this spot, however, many stately trees rose up in self dependent strength and beauty, and expanded in mid air into their complete propor- lions, or, if they sought companionship, they did mot woo a promiscuous throng, but cach embraced a single partner. The number of double or marricd trees congregated at this particular spot was indeed remarkable, and, — reeollecting that the Hindoos either select the neighbourhood of such trees as the sites of temples or plant them where they do not grow natorally, and that, in those ages when they flourished over the Indian Archipelago, the sfrait between Pulo Ubin and Pulo Tikang waa'the portal of one of their earliest and most renowned colonies, Zaba on the Johore river, — it was again difficult to avoid sur- rendering the mind to a belief that the grey pillared and fluted piles, that assumed more and more an artificial appearance as each stroke of the oar reduced their size, were really the remains of some great fane overborne hy many centuries of desolation (1).
It will be borne in mind that the above are firat impressions, and that, having been conducted to one particular locality to see the furrowed rocks, | believed they were confined to it. My next visit undeceived me, and proved that 1 had been nearer the troth when looking for tokens of an internal structural arrangement in the granite, than when conjec- turing the former existence of a cascade; a conjecture which a wider exploration of the same Point would have shewn to be baseless.
I now proceed to notice the rocks at the different places which I have visited, beginning with the Eastern portion of the southern coast afler passing the Quarries, going then to the western division of the Island, and finally returning to the Point where my desire to examine the Island was first awakened.
The seaward extremity of the lateral hill or ridge to the East of the Chinese Quarries is environed by mangroves.
The succeeding point advances out of the mangrove fringe. At the W. side a large moss of eolid granitic rock of a greyish colour, varied by light brownish red (and consisting of qrey felspar and transparent quartz with some black mica interspersed) stretches transverse-
(1) The Extract from my Journal included in the paper alluded to at p. 3 atopa here. ‘
ly along the beach, from which it rises a few feet. Tho beach at ifs base is a band consisting of the upper edges of soft semidecomposed vertical laminae, Further on another mass has its face composed of solid, slightly projecting nuclei of different shapes, wilh lami- nae between, The nuclei are similar in composition to the preceding rock, but in the lami- nated portions the black mica is so thickly interspersed as to form about a third of the whole. A quartaose vein about an inch in thickness traverses the face of the rock, cut- ting through both the solid aod laminated portions. Beyond this extended tabular rocks occur, along the flat surfaces of which fissures and divisional lincs run in a direction NE. by N.... SW. by 5S. A portion of the surface is covered with a ferruginous yesicular crust, volcanic in appearance, The next considerable rock is a ledge running out into the sea, about 80 fect in length and 6 to 6 in breadth, A portion of it is marked by a net work of confemporancous veins of a larger grain and more micaceous than the body of the rock; at some places the veins send tongues into the latter. This structure is analogous to that which the more decomposed rocks consisting of solid, nuclei and laminated curved bands ethibit.
Along this coast wherever the junction of the rock with the superjacent soil of the hill side is visible, there is, im general, an irregular band of angular fragments of the former partially intermingled with the latter, evidently resulting from the slowly descending disin- tegration of the rock; at some places however a layer of rounded pebbly stones is imterpo- sed between the broken surface of the rock and that of the soil. An example of this occurs here. The pebbles are chiefly of three sorts,—a_ porcellanous rock probably semidecomposed granite and syenite — brownish red ferruginous rock, — and jaspideous, The first is by far the most abundant. On the beach in the vicinity are mumerous pebbles of the same description, and also some rounded scoriaceous slones similar to those which are so common in Singapore.
As the SE. angle of the Island is approached, regular spherical nuclei with concentric spherical laminae are found. The most remarkable point in the character of the rock where it assumes this structure isthe abundance of black mica, which indeed constitutes the entire mass with the exception of a little felspar which serves as a basis. It is to this circum- stance that the tendency to this peculiar arrangement of the crystals is in all likelihood owing, The predominating rock around these laminated micaceous globes is greyish and faint greenish quartzo - felspathic, with minute particles of mica and hornblende interspersed. In decomposing it takes a rusty colour, It is obvious that the weathering of such globular fo- liated portions of a compact rock, in situations where the whole was less preyed on by the sea, would give rise to cups and spoon shaped cavities on the surfaces of the more compact masses, and that rows of such spherical portions gradually excavated would ultimately as- sume the appearance of grooves like those formerly described (1),
The SE. point has at one place the appearance of having been subjected to the action of heat since the rock was formed. The sides of cleavage fissures have a blackish brown fer- ruginous liue and a thin bard laminae or seam having the same character sometimes Gills
=(1) Ante, p. 5, 6.
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them. Some veins of a similar substance are vesicular. I believe, however, that this appear- ance has resulted solely from the iron contained im these portions of the rock. Clos to this is a band, about & feet in breadth, of vertical laminae half decomposed and with crus- tated projecting edges. Internally it is composed of crumbling felspar having minute scales of mica scattered through it. Towards the surface the hue is rusty and some deep black stains occur throughout.
Near the point the rock exhibits great variety in its composilion even within a small compass. One specimen has a greenish grey sacchariod felspathic base in which crystals of quartz and mests of mica are sparingly disseminated. Another is somewhat similar, but the base is a dark brownish grey. In others whitish felspar and black mica and hornblende are united in different proportions, equal and well separated, or more finely granulated and mingled, so as, when the mica is absent, to approach to the character of a sycnitic greenstone.
Among the other interesting cxamples of varying structure and composition at the Point there are some solid blocks of a rudely globular shape, with the rock in the spaces between in foliac from 1-6th to 1-8th of an inch thick. Adjoining these are some blocks which, within a circuit of a few feet, change in their appearance and compoution, passing from a black doleritic rock into a well crystallized compound of hornblende and felspar (syenitic dole- rite) in which the former is greatly in excess, — into a similar rock in which the felspar qreatly increases and which at one place is intersected by a rhomboidal network formed by felspathic veins crossing each other, — and, lastly, into a whitish grey rock similar to that around the globes before noticed. The crystallization between the opposing convex sides of adjoining blocks exhibits yet another and still more strongly marked variety, beeom- ing abroptly very coarse, so that some of the specimens which I took fromthe line of junc- tion have, on one side, cither a granite as minute in its granulation as fine sandslone, or a compact dolerite, and, on the other, erystals of felspar and scales of mica of an un- usually large size.
A little beyond the SE. angle there is a band of semidecomposed rock about 2 feet broad consisting of small globular and cuboidal bosses, from 3to 6 inches in diameter, of a very fine grained granite or eurite imbedded in, and protruding from, yellowish white clay. The former are composed of minute micaccous and hornblendic grains thickly disseminated in a base of granular quartz and felspar. It so strikingly resembles fine ground pepper, capecial- ly after decomposition has commenced, that it may be called pepper granite. The latter has originally been in great measure felspathic.
At the SE. Point the slight superficial depressions marking divisional planes, tho prin- cipal fissures and chasms, and the longer sides of separate ledges are all in NE.-SW. lines, or lines not deviating far from these directions. The first have given rise to the two last. The cohesion of the rock at the divisional plane, originally least, is further weakened by partial decomposition along that line. The alternations of temperature from exposure to the rays of a burning sun succeeded by immersion under the waves, and the removal of support on cither side by the mechanical action of the sea, cause the rock to split along the plane, aod thus a fissure ‘is formed. A ledge or band between two f- 23" pe. 1847, B.
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sures i¢ either broken up mechanically by the waves, or wasted away chemically from being more susceptible of rapid decomposition than the adjoining bands, and thus wider fis- sures or chasms are produced.
There is a small rocky islet or group of rocks near the SE. Point of P. Ubin called Skodo, from a fancied resemblance of one of the blocks to a frog. Those in the middle are large and connected by sand in which some shrubs grow, and those geattered around are smaller and much worn by the waves. Some large rocks also lie in the sea on the south side of the central collection, and the longer sides of those run SW. by W., NE. by E. Parellel reddish lines or bands about 44 an inch broad traverse the surfaces and mark the planes of weaker cohesion. The sides of some of the blocks are peeling off in parallel layers. In some, another set of divisional planes, transverse to the former, are well marked, Where the rock is breaking down, these two systems of planes divide it in- to rhomboidal fragments.
The rocks are of a large grained granite, and are im fact the best specimens of well mark- ed and regular granitic crystallization that I have seen around Pulo Ubin, The hornblen- de instead of being collected in nests of small granules intermited with felspar, or disse- minated in minute particles, as is generally the case even in the most highly crystallized rocks of the Island, is ‘here im well defined crystals of various sizes and mostly of a fibrous structure, Mica is present of a fine lustrous black colour with a faint blush of red. Nests occur from an inch to a few inches in diameter composed principally of finely granular hornblende intermixed with a lesser proportion of felspar and containing occasionally a crys- tal of mica,
The eastern end of the Island, in place of contracting to a mere point like the western, presents a coast of considerable extent, This arises from the eastern portion of the Island consisting of two hill ranges, with a flat mangrove tract between them. The termination of the northern range constitutes the NE. Point, The beach is composed of extended tabu- lar masses of rock which slope curvately beneath the sea, and rise only a few feet above it. They are crossed by fissures and small grooves, the direction of several of which is 5. by SW. All the principal lines have a general direction towards SW., although they vary within a small range. In these a row of circular cavities lined with a ferrugi- nous crust somelimes occurs; and where this is the case, the surface of the rock basa semi- calcined aspect.
The rock varies, but is principally composed of an opaque bluish grey saccharoid fels- pathic and quartzo felspathic base enclosing crystals and grains of hornblende, and translucent crystals of felspar. It bears a close resemblance to a specimen of Vesuvian lava ineluding hornblende crystals which [ possess. In some places it becomes compact, or the hornblende granules are so minute as to appear like fine black dust sprinkled on snow. Where they prevail over the felspar the rock has a bluish colour. The base has frequently o reddish brown and brownish grey colour, but this is probably the result of incipient decomposition.
Rounding the Point and proceeding westward along the northern coast, the rocks preserve the same character. They are traversed here and there by rifts, and marked by fissures or grooves of a greater or less depth, but mostly shallow. Where I noted the bearings of
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the divisional lines, those producing the rifts on the faces of rocks sloping abruptly into the sea were found to be cither nearly 5S. or §. by SW., and dipping casterly. Those producing the slight grooves crossed the others, dipping to the westward, and with a SE, bearing. Another system traversed the faces of the rocks in a horizontal direction. The action of the weather and the tides had deepened many of these fissures, so as to form an irregular system of shallow channels. The rocky shore to the south and west of the Point is, like all the other projecting portions of the coast, the basco of o hill’ Off ils western extremity, (which is separated from the eastern by a small tract of mangrove and is per- haps a distinct hill) there is a large insular rock. The external form of this islet is very plainly due to the divisional planes of the rock. Of these the principal are parallel to its N. and §. or longer sides, bear a very little 5. of E. and dip at an angle of about 45° to the 5. Henee while the south edge of the islet has a smooth slope, being formed of the uppermost layer produced by these planes, the northern side on the contrary is steep and rough, presenting a series of broken ledges rising over each other and dipping inwards. The surface of the rock is indistinctly marked by lines at right angles to the principal ones. At the western end, where the remnants of some of the layers stretch into the sea and are broken up by the waves, they are divided by these cross planes imto irregular fragments. Other lines are occasionally distinguishable, running NE. by N. The rock is very like those at the adjoining Point, but has a greater tendency to a compact hornblendic charac- ter. The Point is succeeded by a considerable tract of mangrove.
The next Point is the steep narrow end of a spur covered with jungle save at the sum- mit, from which rises an enormous rock, partially visible through the foliage from the water, With some difficulty I walked and clomb round it through the jungle, and a mi- nute examination on all sides proved that its general external configuration was the result of its internal structure. The northern face, or that which overlooks the channel, is very lofty and picturesque. [ts lower portion is of great length, stretching quite across the hill, and rises to a considerable height perpendicularly, or rather with a slight inclination inwards. Above this wall the rock, as it rises, retires and narrows by successive irregular steps, so as to present a ruined castellated appearance. The nearly perpendicular wall is the face of the outermost of the layers of which the whole mass is composed. Its direction, agreeing with that of the internal planes of weaker cohesion, is E. SE. nearly, but it is slightly curved. The face is marked by two systems of imperfect grooves crossing each other, One set approaches to vertical but dips some degrees to the W. The other approximates to horizontal, but has a dip of a few degrees to the E. Similar markings are found on the southern face of the mass, and they shew the directions of two systems of divisional planes. The eastern side of the rock dips inward concavely, and probably exposes the true form of one set of the divisional planes. On one side the continuity of its surface is interrupted, and ‘the layers assume a tendency to enwrap nuclei. The west foce of the rock dips out- wards, descending by irregular steps. These are formed by two of the systems of divisional silecnie They are much broken and in some places traversed by channels of some regularity which are evidently formed in planes of division, All the planes seem fo be im some de- gree curved.
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The internal structure of the rock not only determines ifs general external figure, but even the vegetation which it supports, Thus the 8. and N. sides, being nearly perpendicu- lar, do not retain moisture, or afford beds for the larger rock -plants.. They have a partial covering of lichens. The E. face is bare. The West face; om the contrary, from it slope, roughness and numerous hollows, retains moisture, and is clothed with a thick mass of dark green ferns, mosses and other plants. The rock is a variable mixture of felspar and hornblende confusedl y aggregated, and from the preponderance of the latter decomposes into a deep red soil.
A very extensive tract of mangrove succeeds, occupying the wedge shaped space between the two hill systems of the Island, or rather, as seems probable, between the two Islands. At a point near the eastern end of the Island a rock 1# exposed which is splitting into small cuboidal fragments. It possesses a twofold mineralogical character, being either a remarkably large grained and beautiful compound of opaque white felspar tinged green, and blackish green hornblende; or a very fine grained black greenstone approaching to basalt, in which the felspar is thickly dispersed in minute granules im a granular base of hornblende. It is oc- easionally traversed by minute veins of felspar. The more felspathie rock is in like manner traversed by hornblende veins. The junction of the two characters in a specimen. is . sudden, but from the hornblende nests in the larger rock frequently resembling the fine grained rock, and the felspar near the plane of junction assuming o greener tinge, the transition does not appear abrupt.
The western point of Pulo Uhin is eminently beautiful. A group of large blackish wave worn rocks advance in front into the sea, and, from the acuteness of the Point, (hence by the Malays called Yanjong Tajam) stand out from the land in full relief, as if they had been planted there to stem the force of the western currents, and defend the Island from their assaults. Behind these rise great masses, with their perpendicular faces sinking into the water, and their serrated summits overshadowed by the branches of lofty trees. The peaks of other and probably still larger rocks are partially seen through the branches and in the forest twilight behind. Rounding the projecting group of blocks the coast presents a succes- sion of noble and varied rocks, here advancing into the sea, there abiding by the land, and sometimes stretching along it continuously like a grey rampart; while over all a glo- rious profusion of many formed, many coloured foliage is spread out in which gay flowers are not wanting; and the massy forest ascends high and dark behind, or, where the rocky wall is broken and irregular, advances some of its mighty children into the breaches. The trees here, as indced almost every where around the shores of Pulo Ubin, are stri- kingly varied, beautiful and imposing.
I have only partially examined the northern coast near the eastern and western points. Not far from the latter there is a very large grooved rock half concealed by mangroves. The grooves are curved in their descent and those at one place in an opposite direction to the others. The grooves face N. by NW. After passing a mangrove tract to the eastward the spur of a hill projects and exposes a broad rocky face. From this plates from 3 to 4 inches thick are falling off. These are composed of laminae from ‘th to y;th of an inch in thick- ness. The direction of the laminar planes is $8. by SE. and they slightly dip to W. by
45
SW. Parallel divisional planes intersect the face of the rock at irregular distances of one, two and more feet, dipping southerly about 45°. The rock is a syenitic greenstone con- sisting chiclly of crystallized felspar in which dark green hornblende is disseminated, fre- quently in aggregations mized with granules of felspar, sometimes the one and sometimes the other predominaling. It also occurs in small cloudy spots and fibres of extreme tenuity in the fclspathic base so a3 to give it a faint varying greenish hue. At the base of the rock are large angular fragments of a dark blackish greenstone similar to that of Pulo Sojahat.
To the east of Yanjong Tajam send the southern shore rocks are abundant. I landed at an open sandy place where there were marks of footsteps and ascended through the jun- gle by a crooked path, half concealed beneath brushwood, to the brow of the hill. Here an acre or two has been recently cleared by Malays who occupy two little hots or rather pondos. Close below on the E. is the bottom of a valley separating this from the adjacent hill, and running NNE. and SSW. The soil is sandy clay and seems to be decom- posed granite of a light reddish colour. Granite very hard and with quarts apparently predo- minaling protrudes at some places, It ia covered by small parallel veins or fissures running E. and W. and SE. and NW. The faces of two of the blocks are very slightly grooved. In the soil are some picees of altered rock like those which abound on many hills in Singapore, and which I had considered altered granite. One piece which I picked up is quite caleined to appearance like the ordinary scoriae of Singapore.
On, or rather in front of, the beach, and within the influence of the tide, there are large blocks of various sizes and from 20 to 3 or 4 feet in height. On the beach behind them are smaller rocks, and further im large blocks again, projecting from the soil of the hill side. The E. side of one of the latter has a singular aspect, appearing as if, to the depth of 3 or + inches, it had been torrified. The surface is rough, semivesicular and blac- kened, the sides of veins or fissures reddish black. The interiour is like the half decom- wcaed acute found in fragmentson Aaynan’s hillin Singapore. The SW. face of one of the large blocks on the beach slopes seaward and is furrowed , but the furrows are not very regular or well marked. This rock is a syenite. It nearly resembles that of Mr. Drees hill in Sin- gapore, but the hornblende is of a lighter green. On the SSW. side of the next large block to the west, the grooves face the SSW. On the sea face there is a deep split or erevise half way through the rock, and varying from 2to @ feet im breadth. Its direction is about NE, by E. The NNW. side of the rock has large grooves which face the SW. nearly. On the W. side there is one groove and on the NW. none.
Beyond this (to the W.) a large flattish slightly conver rock occurs somewhat in external aspect like that of P. Sejahat.
Further W. there is another extended convex ledge. The surface at some places appears as if it had been much acted on by fire, so as to be covered with a rough partially vesicular coaling of altered granite. Where most altered, and also partially in the veins or fissures, it in some degree resembles the ferruginous scoriaccous parts of the torrified sandstones to the S. of Singapore Town. Where least altered the granite resembles the ferruginous fragments of Kaynan's hill. This rock is traversed by two rough horizontal grooves and numerous veins
14
or slight fissures running in the direction of its length or NW. by W. and SE. by E. nearly, a line which cuts the hill of Tanjong Pamoodang on the main. In the lower of the two grooves or channels there is a cup, the surface of which is rusty coloured. Two sharp pivces of rock project from it. One of them is of a very dark green owing to the hornblende greatly predominating. In the cup I also found a globular volcanic stone, semi- vesicular on one side. [t is very heavy, consists of a rusty substance, and exhales a strong chalybiate smell; at right angles to the above there are other splits. At one place, where the beach is formed of decomposing rock, a ledge about 6 inches high and 2 feet broad runs out and dips below the water; originally it was probably harder than the rest but is now soft. It has a whitish and yellowish red colour. Felspar predominates in this neighbour- hood. On the beach altered fragments are strewn. Some are large rounded blocks, which, internally, are of a deep brick red colour. The shore of the next point is strewed with blocks of various sizes. Further in there are large masses, of which some are broken. The Point is the rounded extremity of a low hill (or one of the flanks of the range of the Island) which rises from the beach. Piles of rock are partially seen through the jungle on the hill side. From the W. angle I ascended the slope. A few yards up there is a remark- able mass of rock partially split. The SW. portion, is in its general ontline, as viewed from the SE., a pyramidal block, separated on the NE. from the rest of the mass by an irregular chasm, and, where its base rests on the mass below, also fissured. Its face is grey with lichens and mosses, and so rough with channels as to appear wholly wrinkled. The channels face the SE. and are mostly inclined to the NE., but they are frequently irre- gular, curvilinear, or slightly sinuous. The rock is a syenite, consisting of felspar, dark green hornblende and quartz, — the first greatly in excess.
At the bottom the syenite changes abruptly into a greenish black hornblendic semillinty substance, similar to that of J. Sejahat. At somo places it is about @ feet thick. This was probably the thickness all along the base originally, The fissure between this block and the mass on which it rests runs through this substance, as the upper surface has in some places a thin coating of it. It is broken with great difficulty. I hammered at the edges for some time with no other effect than to knock off the thin coating of decomposed rock , ond had to be satisfied with fragments of some small rhomboidal masses which I found loose in the fissure of junction, The rock decomposes at the surface into a soft yet tough greyish pow- dery substance. The line of junction between the hornblende and syenite could not be mi- nutely examined on account of the weathered state of the surface. I succeeded in knocking off one small specimen at the junction. In this the black flinty rock first passes into a qreensione , then the grey felspar increases (ill the hornblende appears in cloudy spots , streaks and grains, dispersed in a base of felspar. Then in this compound base, erystals of felspar appear. The number of crystals increases till the base entirely disappears. The pa- rent mass is of great size, stretching from the fissure which divides it from the block deserib- ed above to the SE, Beyond this it turns to the NE. and exposes a high perpendicular face, of which the upper half is deeply channelled, and the summit broken info irregular sharp pinnacles, — the terminations of the ridges that separate the channels. One of the channels, the second from the SW. angle, reaches a litthke lower than the others fra-
15
dually shallowing like them as it descends; the sfem of a tree rooted at the hase ascends the face of the rock and enters the bottom of the groove, following it till, as the depth increases, it is lost to sight; at the summit it re-appears and spreads its branches above the rock. At the NE. extremity of this portion of the face, the rock retires a few feet, and then stretches again to the NE., shewing a high quadrangular face with on- ly a few channels.
Facing this side, and at a distance of 15 to 20 yards, a much larger and more regular mags rises in the jungle. The face opposite (and I am particular in noting the directions of the faces, because they appear always to coincide with atructural planes of division or imperfect cohesion) is about NE. by N., that is, mearly the same as that of the rock opposite. This face is nearly quadrangular, and, judging by the eye, somewhat above 30 feet in height. The upper portion exhibits a few furrows, some of considerable depth, but, as the face slightly inclines inwards, these terminate near the top. The NW. and SE. face (i. ¢. that facing the strait or SW.) is more imposing still, It 1 110 feet in length and. about 40 in height. Lt is slightly inclined inwards, and is exfoliating. The upper part alone shews two or three furrows, a few feet in length. It is surmounted by a thicket of shrubs. The rock is a syenite, white felspar in general constituting the great bulk. In some places portions of it have a light greenish hue. The hornblende is irregqulary dispersed , generally in a state of confused aggregation, and sometimes mixed with felspathic grains, but frequently also in long drawn streaks and seams. At one place it was much in excess as to give the fractured surface of the rock a very peculiar variegated appearance , blackish green, light green, and a light iron hue, being variously intermixed with a lesser proportion of white and greyish. On the SE. side the rock slopes to the ground so that I was enabled to climb to the summit and examine it. It is throughout more or less fur- rowed, but the furrows are irregular in their sae, positions and directions, and do mot approach to the symmetrical or artificial appearance of those on the sides of some of the rocks. About the middle of the rock, from the bottom of the slope on the SE. to the edge of the opposite or NW. side, there are some well marked divisional lines running NW. by N. nearly, but there are others less marked at various angles with these. The rough holes and qullers on this part generally follow the same direction, which is also that of the general slope. Towards the NE. face the summit slopes in that direction, and the hollows take the same course. Some of these are prolonged in channels which descend the vertical NE. face, which is of considerably less height than the SW. The cxamina- tion of this rock satisfied me that the slope of the rock, and the direction of the structural planes of imperfect cohesion, determine the direction of the channels, and, this being the case, the conclusion scems inevitable, that rain has been the great agent of erosion. On the SE. face, where there is a gradual slope to the ground, the hollows cover the whole sur- face, but are irregular, because there the rain torrents descended with less impetus, and their action was not greatly aided by the gravity of the masses on which it acted. At some places it has worn depressions of considerable depth and breadth along a line of division, but, owing probably to the occurrence of portions of rock of a different and less decomposable arrangement or apportionment of ingredients, these are separated by solid walls or small
16
fissures. Occasionally a small channel has been worn through the bottom of these di- viding walls.
On the SW., where the structural planes are inclined inwards and the sheets of rock between them are falling off, there are only a few well marked grooves at the upper edge. At one place where the rock has less deeply exfoliated on one side of a cross divisional plane (i, e. one perpendicular to the face) than on the other so as to present a side of a few feet broad at right angles to the face, a channel, about 8 feet deep and 1 foot broad, opening on this side and parallel to the face of the rock, shews clearly that here a portion of the sheets has been loosened, split, and then fallen out, The botfom has afterwards been worn concave from its serving os a rain channel.
The NW. face, so far as the rock continues nearly perpendicular, presents deep fur- rows, and, when it inclines inwards, these disappear.
The NE. face, being perpendicular or slightly inclined outwards presents channels from the summit to the base,
The NW. and SW. faces may have originally been grooved to the bottom, as «the channels are (on the latter very obviously) decreasing in length by the gradual exfoliation of the rock in planes which intersect them. The lower surface is fresh. Where the chan- nels exist the rock has a black, grey or hoar antique look. If the channels are altogether owing to an operation which is still in progress, the period required to produce them must have been very long, os the weathcring now going on must be extremely slow. The surface is coverd with such a close vegetable covering , that it must, in great measure, protect it from the mechanical action of the rain. Descending a little to the east of the spot where I had entered the jungle, I examined some large syeni tic masses which rose from the beach. One of these was divided by a chasm, and on one side, to the breadth of a foot or more, and on the other, to the breadth of 8 or 4 feet, the rock was a black hornblendic basalt incli- ning to flinty, similar to that before mentioned. This must originally have been a connec- ted zone or dvke about & feet broad. The basalt has been freshly quarried and this at one limited place exposed the line of junction of the two rocks. It is sharp and well defined, and on each side the rocks possess precisely the same character which they have at a dis- tance from it. Some of the fragments lying around, however, exhibited the two rocks blen- ding at the line of junction somewhat in the manner of the specimen mentioned above p. 12, but frequently thin laminae of the basalt penetrate the crystallized portion of the rock. From the very variable nature of the syenites and voleanic rocks of this Island, and the abruptness wilh which the proportions of the constituents of the same mass offen change so as entirely to alter its aspect, [ had been previously led to suppose, that the whole belonged to one and the same formation, The appearance of this zone at once pointed to the contemporanity of its origin, and I have no doubt that is was formed in the mode suggested by Mr. Damwis (1), vie. by the opening of a fissure in the syenitic mass while yet viscid into which the most fluid ingredient, hornblende, drained from the sides or rose
(1) Daawis on Volcanic Islands, p. U24
17
from below. The basaltic rock is intersected by three systems of parallel planes of imperfect cohesion, which divide it into rhomboidal pieces, the sides of which are while, owing to a slight superficial decomposition, Of these systems of planes one has a strike NW. by W.. nearly, amd is almost vertical but with a slight, dip easterly. Another runs NE. by E, nearly, and deviates more from verlical fo the SE. by $. than the other,
Proceeding along the beach to the eastward [ found a large mass, on the SE. side. of which was the remnant of a basaltic dyke which was marked by a few horizontal grooves. The face of the remnant is cavernous, and looks as if rt had been torreficd. Further on I noticed a small portion of basalt adhermg to a large syenitic block. The next noticable rocks were some masses of soft semidecomposed syenite with the surface to some depth ye- sicular, This possably due to the contiaued action of the waves and the almosphere.
To the E. af this T found on the beach a small globular rock, 2 to 4 inches in diameter, of a volcanic appearance. Extermally it bad a smoolh enamel of a reddish and blackish brown colour. This is succeeded by a red and reddish yellow band from % to 4, of an inch thick, Internally it is a uniform finely vesicular mass of a dull brown hue and wilh a portion drusy, Near this the beach was plentifully strewed with small stones, many re- sembling those found on some of the Singapore hills, and amongst which ferruginous fragments of scmidecom posed rocks , granite, syenile, greenstone ete. can be recojmuized.,
The hilly point was succeeded by a mangrove flat, which confinued till we reached the point opposite the western end of Pulo Tam. The mangroves fringe the point which is the extremity of a hill of a brownish red soil without any rocks exposed. The soil appears to be deep and tolerably friable, The forest trees are tall and luxuriant, but many of the finest have been felled by Chinese woodeutters, by whose tracks. [ was enabled easily to ascend the hill.
Beyond this Point, and along the greater portion of the strait of Pulao Zam, the coastis a mangrove jungle, There is a small creck at one place, and so far as I could judge from the appearance of the hills on either side it seemed probable, that the mangroves here extend quite across the Island, and that it formerly consisted of two separate islands, The northern coast on the opposite side of the Island is alao the margin of a broad mangrove, swamp Which | observed to be likewise penetrated by a creek. If there is one continuous ereek across there must still be in fact two islands. Towards the E. end of P. Tam, where we again come in sight of the Singapore coast, two lines of high jungle rising over the mangroves mark. the direction of the next hill flanks, The base of the first is wholly en- rdloped by mangroves. The next advances to the beach at one spot where a reddish rock. rises immediately from the water to the height of about twenty fect. The front. alone is exposed. Thr sides are shaded by the jungle, and over the summit is a luxuriant canopy of shrubs and small trees which fairly cntitle it to be called the fertile rock. One of the trees is exceedingly beautiful being covered with a dense mass of dark green glossy foliage which it seems to spread triumphantly, towards the lofticr trees growing around it and. rooted in the soil but less adorned than their sister of the rock. The face of the rock is scaling off. It decomposes into. a deep red earth, and the prevalence of iron which colours the soil probably also gives the dark green to the vegelalion which it supports. The whole
22 pert, 1647. CG.
18
rock is one rudely rounded mass and apparently composed of concentric layers. Towards one side a wide chasm penetrates it leaving at the eastern angle a eolumnar portion di- vided by a horizontal fissure info two rounded blocks of which the upper is still ‘at the top connected with the mass. The neck of junction consists of the remnants of numérous layers wedged in as it were, one half with their conver sides to the spectator or embra- cing the rock above and the other half with their concave sides towards the spectator or capping the block beneath, thus presenting the appearance which a number “of somewhat stiff sheets of paper or other flexible substance do if they are compressed tightly in the middle and their ends made to diverge on both sides.
Beyond Pulo Zam a point occurs from which a large furrowed rock advances into the sea. This I inspected with some minuteness. The channels, even on the same face, run in different directions so that they sometimes cross; but, more frequently, after meeting , one only is continued. In all cases they evidently occupy the lines of division or imperfect cohesion. On the side facing the NW. the direction of the larger ones is nearly NE. and NW. On the S. side they are deep and face the S. These latter it appeared to me had been gradually excavated by the allernating action of the sea and the atmosphere. A little further to the E. the gutters of the rocks faced NE. by WN. nearly; at one place the rock is nearly worn through and the breach is half filled with large angular frag- ments, the remnants of the layer or ledge which had originally ‘occupied the cavity. Its sides are parallel and mark two planes of division. The furrows beyond this were gene- rally in one or other of two directions according to the slope, that is either facing the NE. by N. or WNW. nearly. The general surface at some places 1s uneven, which oo- casions varying slopes, and it appeared clear that the directions of the furrows at these places were fully explained by the directions in which the slopes would cause the rain currents to ron down them. In many cases, the latter did not exactly coincide with the former , beeause no fissures or lines of division did. But of the two systems of parallel divisional lines by which the surface was intersected, that which most nearly agreed with the slope had given their directions to the gutters. Where the face of the rock was slightly hollowed the gutters converged. The ridges between the divisional lines are sometimes crossed by gutters but only where this would be rendered necessary for the descent of the water.
It was not until I had examined both the eastern and western portions of the Island that I was able to revisit the point where my acquaintance with it had commenced. It proved that I had seen only one small section on the 5. side, and that the SE. and E. faces possessed the principal rocks. These stand in great profusion along the beach or rise from the water in front, while the hill behind appears like some ancient »eastled steep" with remnants of flanking walls midway up, and broken battlements frowning from the summit. Many of the piles are ona grander scale than any that are found elsewhere; they have a prea- ter air of antiquity; and rising as they do in diversified forms, — here in solid cubical masses, there traversed by deep chasms and bristling with sharp pinnacles, at one place standing out in fall relief in their grey mossy coating, and at another covered with ao trellis work of roots, trees ascending from their summits into midair, and the entire rock buried under
9
a load of varied vegetation, — the effect of the whole is at once picturesque and imposing in an extraordinary degree. I can only afford to notice a few of the most remarkable rocks, although a faithful description of the whole is desirable, since the Chinese quarrymen are proceeding so rapidly in their work of destruction that it is to be feared these grand and singular natural phenomena will, in a few years, have been entirely obliterated.
One of the most striking of the rocks is a connected pile of great bulk and extent which stretches from the base of the hill across the beach into the sea. It is cleft in a few pla- ees by narrow dark chasms, three of which, in particular, divide it into four principal por- tions, The inner is a great cuboidal mass based in the land, and its sides, being very slightly furrowed, rise perpendicularly like solid walls. At the NW. angle rises what may be called a great columnar turret, partially severed from the mass by a deep narrow chasm, and traversed from top to bottom by deepchannels divided by narrow ridges, and with its sum mit ascending some yards above the level of the pile. A tree rises from. the pinnacled sum- mit, and the whole of the western side of the columnar mass i reticulated by its roots. The principal of these run down the channels to the ground, and, as they descend, give out numerous lateral branches which closely embrace the rock, following its sinuosities and entering the cleft between it and the main mass. The roots are so numerous and 60 interlaced that they conceal the greater part of the rock; and, towards the summit, where they converge beneath the trank, only some narrow portions of the ridges are visible, These differ so little in shape and colour from the roots, and are so closely united with them, that, from some points of view, the whole appears os the solid stole of the tree. From other points of view some of the acicular summits of the turret are free from the net work of roots, and others pierce through it. One of the long nearly horizontal branches of the tree which stretches seaward above the pile is literally covered with air plants save at its extremity. The second mass of the pile is also cubical, but distinguished by a bulky awkward looking protuberance, which rises above it towards it edge and leans to one side, but for which it is imposible to find any architectural prototype. Its rounded shapeless edges and partially depressed sides give it a form more reembling a bit of ginger root than anything ever shaped by art. The W. side of the mass above which it rises is traversed by a few fur- rows nearly vertical, but dipping a little from N, to 5. The upper portion, or about two thirds, of the east side t* rather more furrowed. The lower portion bulges out and is smooth. The furrows incline to the southward, bending more decidedly in that direction as they reach the bulging portion of the rock, on the upper surface of which they termi nate. The third portion of the mass is smaller than the preceeding; and its upper surface slopes seaward. Its sides are much channeled, The upper portion of the southern face of the fourth or external mass slopes curvately from the cleft that separates it from the preceeding mass till its lower portion approximates to vertical and dips beneath the sea, Its surface is on all the three exposed sides on uninterrupted series of sharp ridges and included furrows which wary in depth and breadth. The depth is from two to five feet. Some are broad and deep semicylindrical concavilies — the surfaces of which are grooved or fluted all round. The grooves are continucd without interruption, and with all their regularity of form, beneath the level of the sea where they are quite
a covered ‘by shell fish. The axis of the grooves on the front. rons NW. by W. and SE. by ‘©. nearly.
At the SW. side there is a curious ladle shaped cavity of which the bottom is flat ond about a foot in depth. A channel leads info it from the upper edge of the rock and ane ther, very shallow, descends from it. On one side is a small heart shaped hollow, A band of black hornblendic rock traverses the upper part of the cup and includes the hollow. ~ "Phe appearance of the whole mass from the sea is very remarkable, The summit seema to consist of numerous peaky, the lower being the projecting extremilics of the ridges, and the higher rising well aboye the mass like turrets, while the tree spreads ils arms preter: ingly over the wholo.
On the vertical surface of an adjacent rock there is a deep cup like depression. The @hinese have partially broken the rock at this place, and below the surface of the cup it t# secn to be arranged in concentric foliae corresponding with the cup.
A little to the E. of the pile above described, a large wedge shaped rock rises out of the sea. Ut is furrowed on all sides.
Halfway up the hill behind, there is another very remarkable mass, the face of which stretches along the hill in a horizontal direction for apparently 150 to 200 feet, and with a height in some places of 40 to of fect. A peculiar feature of this rock is, that, while the western portion is grooved vertically, dhe easterm is traversed by a sericea of parallel clefis or fur- rows dipping from E. to W. at an angle of apparently about 46°. The belts of rock be- tween them are broken through in many places by irregular channels often approximating to verlical. The surface of this side as further back than that of the rest, and as a small projecting portion of its wpper edge, which is continued in the same plane with the latter, presents verlical channels of similar dimensions and aspect to those which mark it, I con- clude that after the whole face of the rock had been channeled out, a tabular mas bere fell off leaving only a portion where the cohesion was firmer, and that the next layer or laminae, possessing a different structural cleavage, bas been since furrowed in the di- rection of its principal divisional lines. This conclusion is strengthened by the circumstance that this portion of the face has an angular broken appearance, and that neither its inclin- ed nor ifs approximately vertical channels have the smooth regularly curved surfaces which characterise the grooves of the rest of the rock in common with the other masses in this locality. [Tt is to the lattér, like the first rude angular outline shaped by the sculptor to his finished work, Nevertheless it also bears the impress of a high antiquity being covered by vegetable inerustations, and embraced by the reticulations of the roots of a tree similar in species to that before noticed. Many of the principal roots run along the bands or ridges between the grooves. Some prefer the latter, and some pass from one groove to another by the gutters which intersect the dividing ridge. The summit of the rock presents a dense mass of veyelation.
On the top of the hill, which is here very steep, there are several piles of rocks wlyose perpendicular sides project from the declivity, while their summits are nearly on a level with that of the hill. Ome of these is divided into distinct entire masses by wide vertical chasms. The perpendicular faces are grooved. Another adjoining pile, on the other hand,
has been broken wp into a number of ewhoidel blocks, and long tabular masses resting on these. The passoges between the former are in many places broad and deep, and, where they are covered by the superincambent rocks, form dusky cavernous hollows, which ore tenamted by hats, Some of the external passages are like doorways being about 7 feet im height ‘ond 6 across, Al the side of one of these entrances half of the horizontol eorface of one of the supporting rocks is exposed. It is hollowed out into a shallow basin about 4 feet in dia meter and 6 inehes deep, which is filled with vegetable debris and water, Une of the hori- zontal tabular masses is about 30 feet long. On its under surface, which is smooth, are two semiglobular hollows. An adjacent mass is about 40 feet in length, and 8 in breadth. On its wader surface also I observed a cup about 4 feet in diameter and | in depth at the centre. The hill is here very narrow and slopes steeply on the inner side to a man- grove flat. On this side there are also several rocks. One of comsidcrable size had o smooth rounded surface unmarked by any furrows.
The rocks along the beach, olthough with a few exceptions mot remarkable for their size and archifectural features, are geologically interesting. At the farthest Chinese hut to the eastward are broad flat masses stretching across the beach, and only a few feet im height. Their surfaces are traversed by parallel reciilimcar fissures and slight grooves, marking divi- sional planes, and the direction of these, and also of the longest edges of the rocks, is almost duc NE, and SW. Proceeding along the beach to the westward, a finc example of com eentric or parallel curved exfoliation oceurs. Of what has onginally been on extensive mos of rock there only remain a few solid blocks, of cuboidal and rudely spherical forms, which rise from the decomposed and semmidecomposed bed worn down mearly to the level of the beach. Embracing the rounded bases of these nuclei, and forming the bed, are the upper edges of parallel curved laminae, which continue till those spreading out from an ndjacent nucleus meet them, Sometimes the same laminae are seen, after embracing the end of one block, to bend reversely and embrace another nucleus, so that the surface or horizontal sec- tion exhibits a series of narrow parallel S. shaped bands. The variation in the curves according to the form of the sides of the nuclei is very great and striking. The lower corner of one of the blocks is conical, and the concentric sheaths or caps have the same shape. In the triangular spaces left where three systems of laminae meet, are prismatic masses, solid but of a crumbling structure, and in composition similar to the laminae.
Near one of the Chinese houses [ observed that the face of a rock, [reshly split by the Chi- nese, was a regular curve, and on the hill the side of a large rock had a similar curve. L partially re-exmined the rock mentioned ante, p. 7. The W. side is marked by deep * grooves, of which the axes are NE. by E. nearly. The planes in which these are formed also determine the direction of the face of the rock overlooking the channel. Maty of the qrooves on the west side are a sucocssion of decp pear shaped cavilics. 1 think there can be no doubt that these are owing to sheathed nuclei having been gradually excavated. That such nuclei are very abundantly dispersed amongst the rocks is evident.
A littl to the W. of this rock and towards the beach there is a large flattish rock. One side is a curve in which parallel laminae, after retaining their continuity for some thickness, part im the middle and give off two systems perpendicular to the first. If this
rock, which is nearly buried in the soil, were exposed to meteoric action, a deep groove woold soon be formed in the line were the laminae part and bend inwards,
The metallic vein formerly noticed runs NE. by E. The whole rock is traversed by other planes in the same direction, as appears from slight scorings on the surface. Another princi- pal divisional plane is SE. by 5. a3 is well seen by the direction of the edges of some large rocks adjoining.
To the SW. of the grooved rock first described, the rocks on the beach are either extended and flat, and a few feet above the level of the beach,—or, were worn down nearly to the level of the beach, they are broken into small cuboidal and spherical fragments disposed, where this has been recently done, in regular lines. It is obvious how readily rocks. with such a structure may be worn into cavities and channels,
Having now sufficiently gone into details for the scope of this paper, it remains to explain the conclusions to which I have been led by my observations. In truth, however, I have not much to say on this subject (save what is of a general speculative nature) that has not been anticipated in the second portion of the preceeding remarks. The first circum- stance worthy of note is, that the observer after he has partially explored the Island is wholly unable to conjecture, at many of the Points, whether the next few paces along the shore will bring him to a granitic, a syenitic, a dioritic, or a basaltic rock, or even whether the mass before him, although at the place where he has broken off a fragment decidedly a granite, may not in other places. be found to consist of any or all of these other minerals. The Island, in its general mineralogy, seems to break through all arbi- trary distinctions of plutonic and voleanie, and to confirm, in a very striking manner , the conclusion, to which most geologists have arrived, that these great classes of rocks are essentially similar in origin. The difference in structure, as between a compact basalt and a crystalline granite, is referred to the difference in pressure to which the basalt, cooling near the surface , and the granite , cooling at great depths, were subject at the time of their solidification. That this may, or rather must have a great influence is certain; but the occurrence of such rocks as these of Pulo Winn cannot be explained by difference of pressure, and, indeed, proves that there are in mature causes independent of variations in pressure, adequate to the contemporancous production of rocks belonging both to the volea- nic and the plutonic series (1). Under whatever circumstance: the pranite of the Island wai produced, under the same circumstances were the syenites and greenstones also produced; and some other cause than great difference of depth and consequent pressure must have determined the mutations in the mineral character of the mass. But if it be cerfain § that such cause existed, would not that cause of itself be adequate as a general origin of the differences in igneous rocks attributed to inequalities of pressure? Mr. Lrete (perhaps the most distinguished of our English writers on geology, whether we consider the originality of his views, the philogophical spirit in which they are generally conceived, or the graceful sim-
(1) Mr. Erte confises the term plutonic to granites (Alementa vol. 1. p. 15 and vel. Il. Chap. 32.) and I here wie ib ip the same sense. Olber writers, aod perhaps Mr. Greece himself occasionally, give it o wider meaning.
plicity of the language in which they are expressed) in the Chapter of his Elements in which he treats of the plutonic rocks, and in which he refers them to a deep subterranean source, quotes the following passages from Dr, MacGutroon's System of Geology.
»The ordinary granite of Aberdeenshire is the usual ternary compound of quartz, felspar, and mica; but sometimes hornblende is substituted for the mica. But in many places a variety occurs which is composed simply of felspar and hornblende; and in examining more minutely this duplicate compound, it is observed im some places to assume a fine grain, and at length to become undistinguishable from the greenstones of the trap family. It also passes in the same uninterrupted manner into a basalt, and at length into a soft claystone, with a schistose tendency on exposure, in no respect differing from those of the trap islands of the western coast.” The same author mentions, »that in Shetland, a granite composed of hornblende, mica, felspar, and quartz, graduates in an equally perfect manner into basalt.” Mr. Lrnu: continues: » in Mungery there are varieties of trachyte, which , geologically speak ing, are of modern origin, in which crystals not only of mica but of quartz are com- mon, together with felspar‘and hornblende. It is easy to conceive how such volcanic mas- see may, at d certain depth from the surface, pass downwards into granite” (1).
This is very true, but although the focts previously cited from Dr, MacGuiocn prove the: easy gradation between basaltic and granitic rocks, they seem aa little reconcileable as the rocks of Pulo Uhin are with the theory of a necessarily deep tartarcan origin of the latter, and less subterranean origin of the former. In Singapore there are blocks of greenstone as highly crystallized as any granite but in which large isolated portions become compact and approach to basalt. In these casea it is impossible to refer the change from a compact to a erystalline structure merely to the mechanical pressure of the superincumbant crust, for such a force must have acted uniformily throughout the whole mas: before solidification. The cause of the variations in the igneons rocks (excluding those which cool in or near the atmosphere), must be chemical or electrical more than mechanical, It is probable that Mr. Danwre, in drawing attention to the established influenee of disturbance in causing certain of the ingredients of a molten mass of different elements to crystallize and separate from the mass, and thereby attain the power of ascending or descending through it to a different level according to the specific gravity of the crystals, has discovered a very potent mecha- nical agent which is subservient to the chemical causes of the gradations in the plutonic and voleanic rocks. While believing, however, that the mfluence of continued uniform pressure (and this implies” the absence of disturbance) will be chiefly exhibited in communicating a homogeneous character to the fluid rock solidified under it, I would not be understood to limit the effect of disturbance to the mere separation of ingredients by their different rela- tive gravilics, It rather appears to me that a very important operation of mechanical agi- tation has been overlooked by Mr, Danwin.
This leads me to notice the next remarkable fealore of the Pulo Ubon rocks, their eobowr dal, globular, laminar and zoned struture, which [conceive to be intimately connected with
(0) Lrene’s Elements of Geology (2 ed.) vol. 2 p. 334.
ak
their varying? mineralogical charactor, and, im fact, to be an effect of the same cause. As the varying crystallization of the rocks pie to reject the distinction of plutonic, and. yol- canic so their structure not only approsimates to that of both those divisions, bat even partakes, often im a striking manner, of that which characterizes some of the principal members of what Mr. Lyre terms the melomorphiec serics. The alternation of beds or zones of different composition, and the approach, where mica abounds, to the structure of gneias, frequently assimilate them to rocks of that series; while the predominance of granitic types, and the general character of the whole rocks, demonstrate their direct origin from igneous fusion. The close approzimation of this developement of igneous rocks af some of its points fo certain poimls in gneisose developments will be more particularly considered in the sequel (1).
Some geologists appear still to doubt whether granite ever has an original conoretionary structure, Thus Sir H. on ta Beene im hia valuable Report on the Geology of Cornwall, Bevon ond West Somerset (p. 460) in reference to the detached blocks, protruding rocks, and hollows called rock basins, which abound in the granitic tracts of that district, anya that, afler having given much attention to the subject, he ia far from perceiving good evidence in favour of the opinion that the globular blocks are owing to an original concrelionary arrangement of the granite. He adds, that after much careful observation he i inclined. to refer the rounded character of a large proportion of the blocks, either scattered over the surface or still existing in the fors of the granitic districta, more to the deeomposilion of surfaces produced by divisional planes than to any other cause. Many of the exposed granite blocks on the Pinang mountains are rounded at the edges, and this is undoubtedly there. the result of mere weathering. That an originally, angular block must disintegrate more rapidly on the edges than elsewhere is evident, for there two facea both subjected to, meteo- Fic action approximate and meet, so that the edge decomposes quite through, and being in, every fall of rain converted into the summit of « pelty waterfall, the same mechanical pro- cess which, on a grand scale, is wasting the clifls of Niagara, wears down the decompo+ sing edge. Bat such an operation would not explain the occurrence of really globular blocks, amd as these are seen om Pulo Ubin in the very act of separating from the original compact masses in which they had been formed, and exposing the concentric coats of which they consist, the fact of granite assuming this structure under certain condilions is matter of ocular demonstration. The fact, however, is not new, for alihough it is not noticed by Lrm:, Pouurs, or any other of our recent English writers on the plutonic rocks wilh, whote works Ef am acquainted, and Sir H, oe ta Becuw ie evidently not aware that a concen- tric laminar strocture had ever been actually observed in granite, it 15 distinctly mentioned) by onc of Weaxen’s pupils, the most able and learned of our few mineralogisis, Professor: Jameson of Edinburgh, in his article on mineralogy and geology in the Edinburgh Ency- elopadia, and it seems to be also well known to many continental geologists. Professor Jamnson gays. » Some granites. are disposed io rounded balls or concretions, which are fram
(1) See Post p. 27.
a foot to several fathoms in diameter. These balls are sometimes composed of curved In- mellar concretions, which always include a harder central mass or nucleus, The © spaces between the concretions are filled with granite of a softer nature which decays readily, and thus leaves the harder central masses heaped on each other, or strewed about. Such heaps, or tumuli, have been erroneously described as rolled masses brought from a distance to their present situation by the agency of currents that formerly swept the surface of the earth. Examples of this kind of structure occur in the island of Arran, Bohemia, ~the Harts, the Fitehtelyebirga , and in other countries” (1).
In the Pule Ubin rocks the laminar structure is seen well defined and unequivocal, In the globular form it is a3 regular as that of trappean rocks; and Mr. Scnors’s description of some remarkable examples of this structure im a resinous trachyte or pitchstone porphyry in one of the Ponsa Islands might be applied verbatim to some of the Pulo U'bin rocks. It is not confined to spherical concretions, however, for, as we have seen, it sometimes occurs in rectilinear tones (2), or on the plane surfaces of cobical masses (4), ond, at other places, in irregular variously curved planes (4). In these latter cases it is not improbable that the nuclei are spherical or hemispherical towards their centres, and that the laminae only be- gan to depart from this form, as the expanding nuclei approached cach other and prevented further independent development. Im such cases it is obvious that the upper portions of the laminae have been decomposed and removed by meteoric or oceanic action, and, sometimes, by both combined. Whether the nucleus in most of these cases where only the upper por- tion is exposed be wholly globular or pass internally into a-cylindrical form I am not at pre- sent able to say.
In a paper of great interest upon the granitic mountain of the Brocken and its seen of rocke” read before the Berlin Academy of Sciences on the 13th December 1842, and of which an abstract is given in the firat number of the Journal of the Geological Society of London, M. vos Bucw refers the external blocks with which the mountain is covered and the con- centric laminar atructare of granite bosses in general, to contraction of the mass on cooling. He gives this view a grand application by suggesting that the body of ellipsoidal granite mountains consisls, like small bores, of concentric layers, each repeating the form of the mountain on a diminished scale, — the whole of this structure resulting from the mecha- nical operation of refrigeration. This structure is well marked in the granites of Devon and Cormeall, which have a stratified appearance, the beds conforming to the surfaces of the achistose rocks when these are superincumbent. Sir H. ne 1a Decue considers that the laminae or beds probably agree in form with that of the original surfaces of the granite masses after protrusion, He ebserved at one place alternating beds of a decomposed and hard granite, and he thinks that the difference of original structure may be dué to a tendency of the
(1) Bdinéurgh £Lacyclopedia, vol. 14 p. 414. (2) ate p. 8 da. (3) «inte p. 10 ke. (4) wate p. 0, 18 &e. 29° pext. 1847, D.
26 whole to arrange itself in false beds coinciding with the surface of the crupted mass. At another place he observed a similar alternation of beds, which, however, in this case ap- peared to be at right angles to the bearing of the granitic mass in which they occurred, Schorl rock and granife were seen in another locality in allernate zones. These phenomena appear to be similar to some of those of Pulo Ubin which we are considering.
Whatever were the mechanical condilions under which the mass of Pulo Ubin solidified from a fluid state, we must admit that to no single uniform causes can we ascribe the phe- Nomena which it presents. Assuming, as I think observation requires, that the whole is of one contemporaneous origin, we must allow that the chemical ingredients of the mass were irregularly distributed, if not originally, then at a time immediately preceeding solidifica- tion. Variable mechanical disturbance may have been mainly instrumental in producing local inequalities in chemical and polar action during the transition from oa fluid to a solid state, and this might have the effect of altracting certain elements to particular places and there exciling particular mineralogical developments. A portion of the rocks beneath which the granite rose may have been melted into it, and varied the relative Proportions of the old ingredients, or added new ones. It is perhaps rash to pursue this subject without an exact chemical analysis of the rocks under consideration. But so far as we can take the ascertain- ed general composition of minerals as a guide, we may enquire whether the passage of the same connected mass from a rock in which mica is cntirely absent into one in which it predominates docs not support the above views ? Gan the frequent substitution of hornblende for mica be otherwise explained? It is true there is a great similarity in the chemical com- position of the different minerals which make up the rocks of the Island, but some power- fol forees must have operated to cause the segregation, in limited spaces, of certain elements from the surrounding fluid mass. Mica is very inconstant in the proportion of ifs ingre- dients, and there are species which approach very closely to hornblende, but evem in these the lime of the latter is represented by potash. Where we find the mica ceasing, and horn- blende taking ils place, we must suppose that in the original fluid or viscid mass lime had been segregated in the space now occupied by the latter.
A circumstance mentioned by Sir EH. pe ca Bacon with respect to the granite of Devon and Cornwall bears materially on this subject. He says that towards the borders of the gra- nilic tracts, — that is where the granite comes in contact with the circumjacent rocks, — it alters ils character, passing from a compound of quarts, felspar and mica to a schorla- ecous rock. The mica first disappears, being replaced by schorl, and then commonly the felspar also disappears, and the rock is converted into a compound of quartz and schorl which are generally aggregated in nearly equal proportions. Sir H. os ta Becne also men- tions that mear the joints by which the granile is traversed, its character alters, and that it is adjoining these joints that the character of the mass at ils confines heeomes particularly quartzose and schorlaccous. In the lower spurs of a granite chain in Pinang I remarked that the rock was devoid of that general uniformity throughout considerable tracts which distinguished the central ridge. It was variable in ifs composition and texture, being fre- quently coarse grained. Quarts was largely developed, and in some places schorl, which I do not recollect having any where noticed in the ridge, appeared in large crystals and fi-
27
bres, Sir TH. pm ca Beene seems to consider that the joints, and the change in the mineralogical character of the rock at their sides must have been produced subsequent to the consolida- tion of the granite, since in many places the same joints traverse the schistose rocks, Would it not be a simpler explanation of these phenomena to suppose that the schistose rocks were heated and consequently cxpanded by the fluid granile, — that the crystallization and solidification of the granite commenced in a band or layer next tha surface where it would sooner cool, and where the contact of the solid schist, the immersion of fractured portions of it in the granitic fluid, and the greater disturbing motions (1) would favour erystallization; — that, under such conditions, quartz and schorl are developed at the sur- face; — that, as the heat escaped, or crystallization advanced, planes of minor tension, ul- timately giving rise fo the joints or planes of disconuity, were produced by contraction, vari- able motion, polar action, or the mutual action of regularly arranged spheroids; that they travers- ed the schistose mass immediately above, because, being heated by the adjacent granite, any effect poduced by contraction on refrigeration, the forees of crystallization, or polar action, would, to a certain extent, be common to both, and extended through the superjacent schists to some distance because a splitting of a solid mass tends to extend itself mechanically and the echist was probably in a state of tension from the upward pressure of the granitic bubble; — that, finally, the gramite being still in a viscid state when the joints were formed, the surfaces of the joints became quartzose and schorlaceous? Why the granite towards the joints should have an exeess of quartz at somo places and of quartz and schorl at other places, is a question as difficult as it is important. It may be considered under two hypotheses, either that foreign ingredients were not intro- duced on the opening of the joints, or that they were. Lf we belicve the joints to have been formed at a period in the gradual cooling of the fluid mass, some time prior to com- plete solidification and while the crystals, whether incipient or ultimate, were in a vis- eid state and admitted of motion amongst themselves (2), we shall then have a separation of the mass into geometrical cubes, prisms etc., in each of which crystallization would proceed separately. If in these cubes we suppose the nonsiliceous elements to have united first with the proportions of silex necessary for the formation of {elspar, mica etc. and the crystals thus formed to bethen attracted together leaving a base of silex for ulteriour consolidation, (as seems to have been the case, from the quart in common granite filling the interstices between the ofher ingredients) then, if there be a considerable surplusage of quartz, we should ex- pect to find it accumulated towards the surfaces of the cubes. Im those cases where schorl accompanies the quartz, some of the ingredients necessary to the schorl, such as boracie acid,
(1) Ut is evident that where the surface of o granitic bobble, swelling up from a vast foid expanse, come in eonlact with aqueous rocks, perhaps of unequal resistance, there mast have been greater and more variable mocha- nical disturbance than in the body of tha bubble.
(2) We must beliero that grasile existed for a considerable period in a transition stale between fluidity and soli- dity i. ¢. as a viscid or pasty gubstaneo, and that the ultimate crystals which solidified wero oot preduced during the early stages of thin period.
8
may have risen in a state of gas or vapour through the joints, But, without resorting to this hypothesis, let us suppose that, from the first, all the ingredients existed together in the mags. The external portion of the cube etc, differs more in mineralogical than in chemical character from the internal. The echorl of the former, compared with the felspar of the latter, has a great excess of alumina and a great deficiency of silica. But this dif- ference i compensated, and the balance of ingredients restored, by the quartz which ac- companies the schorl, If we therefore reduce the intermal and external portions to their constituents, we shall find that the essential difference is only about 10 per cent, and that it consists in the latter having about 9 per cent of oxide of iron instead of only 2 per cent, and in having about 2 per cent of a mew ingredient, — boracic acid. We can hardly err in attributing the difference mainly to the chemical action of the acid, which, whether hy itself or in combination with soda, is remarkable for its fusibility, and its power of com- municaling this property to compounds, The tendency of certain substances in a fused mass to relire towards the surface when other substances are there found for which they have a stronger aflinity than the other constituents of the mass is well known. But there is no difficulty in conceiving that such <a transfer may have been mainly mechanical. The boracie acid may have retained a portion of the matter with which it was in combination in a fluid or viseid state, for some time subsequent to the crystallization aud partial solidification of the felspar ectc., and the internal pressure of the semi-solidified mass alome may have forced this towards the sides and cauged it to rise to the surface. It is ascertained that both felspar and quartz remain in a viscid slate at temparaturcs greatly inferiour to that at which they are fused, and henee there must have been a degree of internal pressure sub- sequent fo crystallization. The fugitive character of schorl is more than once pointed out by Sir Tl. ne ta Becus in his Report. Amongst other instances of alterations produced on sedimen- tary rocks by contact with granite he mentions some slates in which schorl has been intro- duced between the laminae. A more remarkable case occurs im a granite consisting of large felspar crystals in a base of schorl and quartz. At some places the felspar crystals have been decomposed and replaced by crystals of schorlerossing each other in various directions, and ihe schorl in the surrounding bdse is evidently deficient.
The abundance of quarts at the surface may be due in some measure to the circumstance that the boracic acid, whether expelled from the interiowr on the crystallization of the felspar and mica or derived from without through the joints , would, wherever its ullimate locality was, be hostile to the formation of felspar and mica there.
~ However wo may account for it, the fact of the schorl taking the place of felspar and mica in the Devonshire and Cornwall granites, appears to be analogous fo that of horn- blende replacing mica in the graniles and syeniles of Pulo Ubin, and if we extend the prececding speculations regarding the one transition to the other, we shall find them in har- mony with the views formerly expressed. We must in the first place consider the Island itself as the summit of one granitie bubble, of which much of the external portions have disappeared. A portion of the bubble (its superjacent rocks, whatever they were, having heen swept away) is now elevated above the sea, so as to expose a belt below high water mark to the action of the waves which are working info the nucleus, and , in their pro-
29
qress, laying bare the structure of the external layer of the bubble, This portion we must conceive to have been nearer the pre-existing superjacent rocks than the central and higher mass, (which was probably denuded to the nucleus before it was elevated to ils present level) md the great variations in its structure and ingredients may have resulted from that circumstance under the influences previously adverted to (1).
The leading fact relating to the structure of the rocks is, that tho principal vertical or approximately vertical planes of division have a general direction approximating to NE. .») SW. Tt i@ also observable that the tones of softer rock and the majority of the grooves have the same directions. Pulo [bin lies in the great platonic band of elevation stretching from Assam to Banca, and having, from Junkceylon southwards, a south easterly direc- tion. The divisional planes are therefore nearly at right angles to the axis of elevation. Is this a general geological phenomenon? Lt probably is, because im a locality so far remove ed os the south west of £ngland it is repeated. Sir H. ne 1a Beene informs us that the divisional plancs of the granite and other rocks in Cornwall and Devon are generally NNW. ... SSE. The grand conclusion which he draws is, that this direction approx- imates to the present magnetic meridian of the district, and may therefore, in its origin, be related to it. Pre-occupied with this view he has overlooked the fact that this direction ig at right angles to the direction of the principal granite masses of the district (E. 24° N. W. 24 5S. (2) which, beginning at Dartmoor, are continned to the Seilly Islands. Not merely the south western division of £ngland, but the general configuration of the British /siands, seems to be due to axes of elevation having the same or an approximate range. Thus the great body of Scotland and Jreland may be considered as one connected mass opraised on such axes. Professor Purturs (4) mentions that the anticlinal axes of the Aigh- lands and Lammermuirs in Scotland prolonged to Donegal and Caran in freland, ond those of the Cumbrian mountains, the Isle of Man, and North Wales, all range NE. and SW. [t also appears from Professor Pomsurs diagram shewing the result of hia exnmination of the joints in the mountain limestone districts of the north of England, that the great majority of the divisional planes are there in NNW. and SSE. lines (4). A coincident range has been observed in the joints in other localities in England, and also in France » more particularly” says Sir H. om ta Becoe » in granites and grauwacke” (5). I think it probable,
(1) If the views advanced in o subsequent part of this paper are correct, we must recogniee in granitic fluid martes a period, in the gradas] diminution of their temperatore to the fusing point, when the external layer, having jast extended itself into the superjacent rocks by melling them iolo ile substance, won orrested in its further extension by erystallisalion. Weoce the external layer should often be variable, ond parlake of the chemi- eal ingredients of the adjacent rocks, because lime wae mot allowed for their thorough mixture with the general mass. Jn fact this layer most often be meroly wo layer of the adjacent rock fused down and immediately erystalliz- ed into a granile. (See note, p. 33, Fost. )
(2) Da ca Beeme’s Mepert p. 147.
(4) Treatige on Geology Jnod vol. p. 258.
(4) fe. eh vol, p. G5.
(5) Meport p. 275.
a0
therefore, that the jointed structure of rocks will be found to be much more connected with the directions in which igneous rocks have swelled up and been injected, and islands, mountains and continents been consequently upraised, than with the magnetic meridians, If due to mere tension, it may have originated under both or one of two influences. If we conceive, what is most reasonable and consistent with observation, that the formation of mountain chains is accomplished by a slow movement or succession of movements prolong- ed during a great geological period, then we must admit that the upper layers of the gradually ascending and cooling mass have been exposed to continued or repeated pressure from below, which, of itself, would cause the partially hardened or viscid crust to crack, or would give rise to planes of inferiour resistance to tension in which the mass would have a tendency to part. But there is another source of tension which may co-operate with exter- nal pressure, or exist independently of it, amd that is simple contraction after crystalliza- tion on cooling,
In and near Singapore we find the stratified rocks in general clevated into low ranges of hillocks, of which the axes coincide with that of the Malay Peninsula and the Islands from Singapore to Banca. The strata have commonly been tilled up at very high angles, frequently approaching vertical. Considering the Peninsula and its prolongation in the Archipelagoes south of Johore as one band which has been subjected to elevatory plutonic forces (1), the first external effect of these forces must have been to cause o great tension from NE. to SW., across the tone, followed by a rending and displacement of the superincumbent strata, and injection of ignifluous matter along lines at right amgles to that of tension, or from NW. to SE. The principal divisional planes must have been the result not of a transverse tension like the first, but of a subsequent longitudinal ome (2).
The great rending and displacement of the strata, and the circumstance of the heads of adjoining strata being sometimes broken up and intermingled, prove that mechanical movements of great violence, and combining a horizontal vibratory with a vertical action, must have attended their upheaval. The direction of these movements must have agreed with the line of tension, because they were nothing more than the effect of the tension reaching the limit which the rocks subject to it could bear. The strata are generally inclined from SW. to NE., although there are several exceptions. The elevatory force therefore acted, to a certain extent, im this direction. Was there an actual propulsion of the fluid or viscid matter from SW. to NE. or merely on undulating motion in this direction? Such a motion is even now experienced in a slight degree along the western border at least of the Peninsula when the subterranean forces are acting beneath the western border of Su-
(tl) Whether o simuliapeous action eleraled both the central granitic chaina of (he Pentmew/a and the semi- voleanic hills along Uheir base and to the south of the Peninsula, or the latter were due to o later subsidiary atlion conneclad wilh the abiftiog of tha mubterranean forces fo Sumatra, does nal affect tha above reasoning , since the fact of agreement in direction is clear.
(2) See Mr. Hornis’s paopera, Mesearches in Physical Cealogy &o.
od
matra (1). There is a source Iess remofe of motion in the upper portion of volcanic and plu- tonic fluid or semi-fluid masses which I have not seen noticed by geologists. When the superin- eombent strata were fractured in NW.—SE. lines, and the fluid mass pressed into the openings, the adjoining portions would acquire a temporary motion towards the openings or at right angles to the lines of fracture. In all cases of plutonic elevation there must cither be a slow continued motion upwards as the strata insensibly give way to the pressure » OF an accelerated molion when great rents in the strata are abruptly produced. In most cases the viscid granitic mass has probably been of too great extent, and the molion too slow and uni- form, to give rise to any variableness of structure.
If a motion, however induced, of the igneous fluid from SW. to NE. be assumed, the alternations which we find in the Pulo Ubin rocks, in bands running SW.—NE., might perhaps be explained on the same principle by which Professor Foanzs accounts for the viscid mass constituting a glacier being zoned in the direction of its length,—an cxplanation which Mr. Danwis has applied to the lamination of volcanic rocks of the trachytic series. In the ease of the Pulo Ubin rocks, the general agreement in direction between the zones of variable mineral character and the principal joints, renders it in a high degree proba- ble, if not certain, that, if mot contemporancous in origin, the continued action of the same cause superinduced both. This cause must have begun to operate when the mass was in a fluid or viscous state. Now as some zoned glaciers are of as great bulk as many exposed granilic masses, such as those of Cornwall or that of Pulo Ubin, we may safely consider that the influx of a viscous body of gramite into fissures gradually enlarging into qreat cavities, would, at least somelimes, under a certain range of motion, and where the conditions assimilated to those of glacier motion, be attended with mechanical structural effects somewhat similar to those observed in glaciers, and repeated in the experiments made by Professer Fonses on other viscid substances. The conditions under which plutonic masses rist must vary very greatly, but there is no difficulty in believing that they some- times, and particularly in masses of no great bulk, approximate sufficiently to those which, in glaciers, produce parallel bands of variable tension, vertical towards the surface.
Reverling now to the analogies between the rocks of Pulo Ubin and rocks of a decided queissose structure (2), let me request that, in reference to this subject, the preceeding dis cussion be kept in view. Mr. Danwie remarks that such facts as the vertical or highly in- clined lamination of felspathic rocks, such as he observed at the island of Ascension, and which exist elsewhere, » are manifestly of importance with relation to the structural origin
(1) fo the most reeeot instance of an earthquake of greal power, — thal experienced on the west coast of South america in 1335 and the phenomena of which clearly proved the idenlily of platonic and yoleanie power. — the undulations appear to bave proceoded from the SW. oxtending consequently in NW... SE. waves, Mr. Danwis says: » The fissores in the ground generally, though nol uniformly, extended in o SE. and NW. direction and therefore corresponded to the lines of undulation or of principal flexure.”" Danwra's Jourmal ps Sil (2d. od.)
(2) date p. 20,
of that grand series of plutonic rocks which, like the volcanic, have undergone the action of heat, and which consist of alternate layers of quartz, felspar, mica and other mine- rals’ (1). The origin of this series of rocks is one of the great debateable questions of geo- logy. As in so many other instances, both of phvsical and metaphysical questions, where an array of probabilities can be advaneed on each side, both parties may be in the right and both in the wrong; or rather, mature, capacious and multiplex while harmonious, can embrace and assimilate the ideas of both. If we limit our views to Jndia, we can hardly deny an identify of origin to granite and gneiss. Upon the question generally I shall not enter, but it may help us to a better understanding of Pulo Ubin, if- some facts, gathered from the papers of Jndian geologists, be here placed side by side with those local facts wilh which they appear fo be connected by some general law. Dr. Vorset, one of the earliest and ablest labourers in the ficld, remarked, in 1024, — » up to the present time 1 am inclined to think that both the granite and gneiss of India are conlemporanecous, as they are perpetually passing info each other and have the same subordinate rocks. I think it probable they owe their difference of slructure to a different mode of consolidation (3)." Dr. Bucnasas Wasturos’s recently published report on the Eastern Districts of Bengal confirms Dr. Vorsey's view, and suggests still more important considerations bearing on the geology of the Malay Peninsula and ils Archipelagocs. In reading it | was struck with several features of the hill ranges of Bengal which strongly reminded me of those of Singapore. T have been led to think that the same relation subsists between these hill and the great mountain ranges behind them, — between the lower hill ranges on both sides of the Pe- ninsula of Sowtherm India and the central mountains, — between the hills on the flanks of the Sumatra chain and the chain itself, — between the hills along the coasts of the Malay Peninsula and the mountain groups of the interiour; — ond between the hill ranges and the mountains of Awsfralia. Some remarkable characteristics ore com- mon to all these hill ranges and groups, and every addition to our knowledge serves to confirm my impression that they must be referred to one geological cra and one peculiar plutenic or volcanic action operating over a region of great extent, in which Southern Africa, India, the Malay Peninsula, a large portion of the Eastern Archipelago and Australia, are included. It would require a separate paper to bring together the facts that have induced and confirmed this impression. I will here only nolice some circumstances mentioned by Dr. Bucwasas corroborative of Dr. Vorsey's view, and bearing on the structure of the Pulo Ubim rocks. The minerals of what Dr. Bocmaxan terms the southern central division of Bhagulpore consist, in general, of aggregate rocks composed of felspar or schorl intermix- ed with quartz and sometimes with mica, and disposed in vertical strata running casterly and westerly, The quartz is not only found as a portion of the aggregate, but in parallel layers alternating with it, and even in whole strata. »In some of the strata the compo- nent parts were pretty uniformly scattered, thus forming granites, according as they contain-
(1) Dinwtr on ecolcanio Jolanda p. 72. (2) Baswaten’s £Ldinéurgh Jouroal of Science tel. X p. 375.
ed 3 or only 2 ingredients; but in by far the greater number certain plates or flakes, as it were, conlained a greater proportion of one ingredient, and certain portions a greater share of the other, forming thus what by some is called Gneiss. The length of these plates is always disposed parallel to the general direction of the stratum, and the edges are verlical, or nearly eo. ‘There were also other stones, in which the component matlera were disposed in what may be called strine; that is a great proportion of one of its component parts run horizontally through the others in lines parallel to cach other, and to the direction of the stratum. Such stones have also been included under the name of mets.
ein many of these stones may be occasionally found vertical layers of white fat quarts, running parallel to the stratum, and entirely separating ome part of the aggregated matter from the other, without producing the smallest interruption of substance; nor is the stone more easily broken there than anywhere else. Im these stones, when entire, there is no- thing like a schistose, or striated fracture; but in a state of decay, if exposed to the weather in certain situations especially so that the rain may lodge on the surface, the stone gradu- ally splits, into thin plates like slate, and this seems to happen as readily to pure quartz, or to perfect granites and granitels, as to the gneiss. In other cases again, especially where blocks have been detached, the stone decays concentrically and of course, losing its angles firat, becomes a rounded mass (1)j." The rocks of what Dr. Hasnttron terms the northern infermediate division consist also of granites and gneiss.
The recent publication in the Journal of the Asiatic Society of Bengal, of Captain Hensrar's Report his mineralogical survey of a portion of the Mimalayas (2) has shewn that gneiss is the grand constituent of these stupendous mountains, but the gneiss frequently loses its la- minar character and approaches or passes into granite; a species of granitic gneiss is common, which appears very often to form the transition between granite and gneiss. The observa- tions of Captain Henzeat appear to me to tend very strongly to the conclusion that the gneiss and granite of the Jimalayas were of contemporaneous plutonic origin. The gneissoz struc- ture may be simply the consequence of an excess of mica, for in most instances where Captain Heasent notices the occurrence of granite, he adverts to the diminution of the mica. Again, as mica diminishes the laminar structure disappears. Thus at one place the gneiss gradually loses its mica and becomes an unlaminated mixture of quartz and felspar, having the aspect of quartz rock. A rock oceurs composed of felspar and hornblende in different proportions apparently very similar to some of the Pulo Ubin varieties; and at one place Captain IL ob- served it passing into gneiss, although in general the transition is abrupt. It occasionaly con- tains mica and even quartz. Greenslate passing into greenstone occurs frequently. The direc- tion of the principal beds into which the gneiss is separated ((rac strata according to the Wer- nerians and metamorphists,) comeceides with that of the mountain zone of greatest elevation,
(1) Manves’s Aastern Jndia, vol. 2, p, 197. (2) The date of the eurrey is not given, but Captain Hensent was al Almorad, engaged in it when Bishop Home visiled the mountains io 1842. (See Heomn’s Journal). ir 29 next. 1047. E.
34
the dip being to the NE. These strata-like divisions are frequently crossed by fissures at right angles to them, and somelimes by another system in a different direction. In some places, particularly in the higher regions, the gneiss, though perfectly laminar, is not divid- ed into regular beds by parallel seams but is crossed by fissurcs in all directions. In a lower zone, of the Mimaloya a range of granite tracts of considerable extent occurs. This zone is parallel, fo the direction pf the axis of the monutains and the strike of the gneiss. The most eastern tract, at Chumpawat, is soft like the growan of Cormwall, and contains much felspar and little mica, . Hard blocks are strewed over it. A portion of the next mass is exclusively felspar swhich, it would seem, is stratified’, Near Dhoe, Capt. Henseat describes some sphe- roidal blocks of great size, which are exfoliating in the same manner os those of Pulo Ubin. One of these was 60 feet in diameter. Numerous veins, consisting almost wholly of quartz and feslpar, traverse the granite. Schorl abounds. The next mas, proceeding westward, is at Almorah, where granite and granite gneiss occur, A fourth masz is found at Palee which preciscly resembles those to the eastward, Lt appears to pass into gneiss on its borders, On a line to the westward »a rock oscillating between granite and gneiss” is found. Near Dikooess the rock development is so interesting in itself and bears so much on the subjects discussed im this paper that | shall cite Gaptain Hensent's description, sim a geological sense the rock may be called a gneiss, but it exhibits small patches * (forming regular transitions amougst themselves) of the most regolar micaceous schist (earthy type), and, again, of the most legitimate granite (growan). These three rocks, so different in composition, in minera- logical character, and in supposed feological origin, may be here observed in the compass of a few yards all naturally (mutoally? } mterchangeable, while nothing like a veimous ap- pearance cari be altributed to amy of them”. Om the same tone wilh the preceeding masses, but at a great distance to the westward, the Choor Peak, which rites to the: height of 12000 feet, is composed. of granite.
The sone of gneiss is 24 miles in breadth and includes all the higher summits of the fiimalayas. The gneiss was seen at altitudes of from 2,00) to 25,709 feet. To the south- ward succeeds a zone of about the same breadth formed principally of micaceous, chloritic , taleose and hornblendic schists, but including limestone and the granitic tracts formerly mentioned, These types vary excecdingly in themselves, and in their transitions into each other, This schistose tract is succeeded by a band of sandstone which is referred to the New Red. The general dip of all the rocks from the sandstone to the gneiss is from 20° to 30 to the NE. or fowards the great central plateau of Asa, The lowest system is therefore the new red sandstone: ond the highest the gneiss. Captain Hensear seems to consider that this fact negatives the idea that the planes of apparent stratification ore really what they seem, and he is obviously rather disposed to refer them to a similar action to that which produced the fissures transverse to them. Jt is scarcely possible to conceive that a continuous mass of strata, about GO miles in horizontal breadth at their present inclination, which would give an original vertical depth of about sirteen miles, should have been raised on its edge and made to move through an are of 160° to 160° until it rested in its present position, with the gneiss, originally 16 miles below the sandstone, now as many miles above it. Such displacement does no doubt sometimes occur on a great scale. Thus in the Alps, and, os
we learn from the great work of Sie RK. Muncuwson ond M. oe Venxem, in the Ural moun- tains, thick maseeq of ctrala are in tome places overturned, and, on the flanks of the latter mountains, the order of superposition is thus sometimes imverted. But such cases cannot justifiy us! in supposing that in a similar convulsion on a« transcendent scale the Mimalaijas originaled., The metamorphic theory might get rid of the difficulty if it could be shown that the gmeisi and other rocks resting on the mew red sandstone were really more modern sedimentary rocks! (1) Until we possess further light we scem justified in considering that the rasearches aod conclusions of Captain Hearar tend to prove that the passage) of gneiss inte granite or the reverse may be determined simply by the variable proportions of mica and the conditions of crystallization from a common state of Muidify or viscidity. A portion of the Himalayas bas more recently been examined by De. MacCumsaxn, and he declares positively that the granite is stratified, the strata being nearly vertical and appearing to be composed of nodules around which concentric layers are wrapped. We states also that tha qnatss rests on ¢ha granite in conformable strata, ond that the two! rocks pass insensibly into each other (2),
The metamorphic theory starta om a basis of fact and is demonstrably trac up to a cer- tain «limit. But when applied to mountain masses of enormous thickness we leave that limit far behind. The conversion of the Himalayas from soft sedimentary into erystalline matter cannot be explained by the plutonic action of granite on known aqueous rocks, even where it has pervaded them to the thickness of a few hundred yards. If the Himalayas were metamorphosed, the process must have been different, or -platonic influences must have been in operation of far greater ‘potency, and having in some reepects a different mode of action. There is an unsatisfactory want of definitencss about the meta- morphic theary even when expoanded by its great advocate M. Lye, If the ingredients of gneiss, were orjpioally arranged os we find them at present, then it only differs: from the Wernerian theory in substituting a posteriour for an aboriginal consolidation, and places qneie on the same fooling with any of the secondary or tertiary sandstones that have as- sumed a sfony textore since they were deposited from water. On the other hand if it takes a bolder grasp of the difficulty and asserts that the whole structure of the rack, the regular form of ifs crystals, and the separation: of those of differant. species into, alternate laminas, are due to the mass having been melted into a viscid state. and subjected to erystalliation de novo, it appears to come so close to direct plutonic formation that it is not casy to see where room is to be found for a vast metamorphic laboratory on the confines of the latter, Its advocates have probably seen and shrank from the difficulty of defining the conditions
(1) Dr. Bececasn coligntes the thickness of al! the Europenn wtratified reeks lading the primary ol feo miles, Bridgewater Treatioe, vol. 2, p. 39.
(2) M. Cavoun desoribes (he granite in the district of Fennieelly in Southers Jndia os srieing above thewurfate in temarkably globular eonerétions and in perfeet/y atratified maarea™, forming low detached hile near Palem- coatta the strata of which dip at an angle of about 450 1¢ the SW. (Berwsrens Ediadurgh Journal of Science’, vol. X. p. 028). Other writers on the geology of Fndia’ mention the occurrence of granite ia many places with a vimilar appesrance, Wounotet in hie work on Centenl fava deseriber the remarkable slructure of the granity surrounding the masa of the afftar, At Melyvam a large grained granite ia sregularly stratified’.
necessary for the existence of a metamorphic region subsidiary to the plutonic and so won- derfally related fo it that, —while, in all unequivocal instances of change in sedimentary rocks from the neighbourhood of a pultonic fluid, the power of the latter has been confin- ed to the marrow limit which we now see (1) to be altered, or, beneath the present base of the rock, has entirely reduced and transmuted it, — in the region in question the power of the plutonic fluid was so much weaker that the original strata of the scdimentary rocks subjected to its influence were left unobliterated even up to the plane of contact, and yet so much greater that the substance of the entire mass, throughout thousands of yards in thickness, was melfed, re-crystallized and arranged in laminae (2). Until these conditions have been defined and illustrated by facts, it is not unreasonable to suspend our judgment, and fo believe that the tendency of plutonic rocks having the same ingredients as gneiss to a stratified or zoned structure, ond even, where mica is abundant, as in the latter rock, to a laminar arrangement, may hereafter be found to explain the origin of such enormous bedded and laminated crystalline masses, as the Mimalayas exhibit, more simply than the theory of metamorphism os at present developed. .
The beds of guciss are no doubt devoid of that regularity which divisional planes possess, and in this respect resemble strata of deposition, (%) but it appears to me they ore not ana-
(1) Mr. Lrete ia not able to adduce an inslance of alteration beyond 400 yards from tha point of contact, and thia be admila to be an extreme com. Elementa, vol. 2. p. 403 and 411.
(2) Tt in well ascertained that stratified rocks of aw limited thickness may ba melamorphosed by granitic influence wilhout losing their division ioto strata, but tho dificalty is in conceiving a plutonic action oo powerful as to extend to the apper part of a mass of some miles in thickness and reduce it to sa olale of semifasion™ (Lrect’s Eloments 24. vol. p. 411) without destroying all vestiges of the original strata in the lower part. The platonic influence may have been conducted through fissures, but in that cos it would bo necessary to shew that a system of viens ramilios throughout the Afimafayan was, for inslance, almost as complele aa those which distribule the blood throughout the body of an animal. If, os scema probable, there are, belween tha great plutonic tracts of elevalion, extensive tracta auflering depression (auch as thos covered by the Bay of Bengal or the Jndian Ocvan generally) their rocke must be exposed to plutonic influence Igterally on well os from below, and this would reduce the difficulty. Mr. Tract enya that, granite may baye been another reeult of the eame action (i, @. that which produced gaciss by semi - fosing sedimentary alrato) in o higher stateof intensity, by which a thorough fusion has been produced; and in this manner the passage from granile into goeisa may be explained.”* Now when in the, Himalayas we find miles, ond in Scotland great deptha, of gnoies ond ils aswocialed rocks, conlaining frequent beds of granite, it is oot easy to conceive how tho metamorphic influence in ascending through masses of much thickness, should be so unequal as to melt down soma portions, while only half melling the bulk of the strata. In the lower regions this ia quile conceivable, bot when we find the same inequalily io seelions of the mass near the summit, that is many miles in some cases above the level whence the action emanates, the theory aceme to halt.
(3) Loewe's El. 24. vol. p. 390. Tho strongest argument in favour ef tho sedimentary origin of gocies is that insisted on by Professor Prices. He says that ein gneiss ond mica echiel the felepar, quarta and mica are rolled or fragmented tonsa, ashewing clearly that the eryastala had been exposed to attrition previows to their deposit’. (article Geelogy in Penny Cyclopaedia vol, XI. p. 190, and Treatise on Geology Iat. vol. p. 112), Th. in-clear that, anch must be tha condition of the ingredients of sedimeniary rocka derived from the wasting of granite, and subsequently consolidated so as to resemble gneiss, on in those ascertained instances where injected granite has been the agent of solidification, But if the fact be universally true with respect to gneien, ik ie falal to the bypolbesia of the platonic origin of thal rock ia any case. It in a two edged weapon, however,
57
lngous to the divisional planes which alike penetrate plutonic rocks and the strata above them usually in directions approaching to vertical, and which also exist in gmeiss, but to those beds in granite which vox Buea considers as always conforming to the external surface of the granitic bubble, of whatever form that may be, and which Sir H. ov ra Beene describes as being in Devonshire and Cornwall actually parallel to the strata of superjacent sedimentary rocks where the plane of contact can be seen (1).
for it would deslroy the melamorphic theory also. The Treafise on Geology was published in 1837, and the second edition of Mr, Lrace’s Elements in 1841, bat in noticing some objections to the metamorphic theory Mr. Lut does not allude to Professor Parmurs’ argument. It is to be presumed therefore that he diseredils the fact on which it rests, and as | do nob find it mentioned by Prof. Jimesox, who has sludied gneiss carefully, nor by olher writers, wo must waitfor further investigation, Professor Jammsox, on the contrary, in Memaar’s Encyclopaedia of Geography published in 1834 (p. 219) positively states that the concrolions of limestone, gneiss, mica-slate and olber rocks of the primilive class have the same characters as those of granite i. e. slhey are joined together without any basis or ground, and at their line of juncture aro eilher closely altached together or are intermixed ,"" and frequently branches of the one concretion shoot into the other or the concretions mutually im- press cach other.
(1) The study of platonic rocks and of mineralogy appears to have been somewhat. noglecled by geologisla of the English school, and, making due allowance for the influence of Waaxna’s theories, I should be disposed to give much weight to the inferences of tho Scottish goologista who, animated by the ardour first kindled at|Freyterg, during many years laboriously and minutely explored the mountains, coaste and islands of their native eountry. Goeiss is largely developed in the north of Scotland and frequently associated with granite, and the analogy be- tween them must be very strong to admit of Professor Jamesos declaring that. »granite occurs in masses, often rouny miles io exteolt, surrounded by gooies, mica-alote, and clay-alale, and so connected with these rocks, that the whole may be considered as the result of ona grand process of crystallicalion; that is, the granite is of contemporaneous formation with the gociss as the gneiss is with the super -imposed mica-slalo, and the mica - slate again with the elny-slate whieh real uponit. Jn ofher instances the granife alternates in bede, often of enor- mows magnitude, with gneiss, mica-slate, clay-alate, and other primitive rocks, or it traverses theese in the form of veins.” Again, >granite is sometimes disposed in great beds in gneiss ond olher rocka, and occa- sionally these beds appear divided into elrala. In olber instances, in granite mountains we observe besides the tabalar, globular and other structures, also tho stratified; bat this latter is, in general, loss perfec! than, what is observed in gneiss and other rocks’. It is true Professor Jameson then believed in the M¥ermerian, theory (which he has since largely abandoned, for in his Intost classification he distributes the hypogene rocks into Plu- tonian and Neptunian) but he would not misrepresent facts, and the facta which he observed in Scotfand seemed to him to demonstrate the derivation of granite and gneis from o common origin. Now thie conclusion is quite separable from the ulteriour speculation as to the nature of the origin, aod in the present advanced state of our knowledge it seems to require us to substitates platonic for an aqueous, without tho intervention of the melamor- phic, theory. Let me not be understood however az desirous of embracing a direet plutonic theory in the place of the metamorphic. All I maintain ie that thero ia a limit whore it ceases to be w theory and becomes an hypo- thesis, and this limit is narrow compared with the vast province over which ils leading exponents extesd if, de an hypothesis it is highly valuable, having alroady guided investigalions which have been rich in results, Its ie- gilimate domain, of which the boundaries are defined by geological demonstration, is constantly enlarging ; and, in the present palmy condition of the science, we may hope thal geologists, in a few years, will be blo to determine whelher tho bulk of what are termed the primary or hypogene stralified rocks be semi- plutonic (i. metamorphic) or entirely plutonic. in the same sense in which granite is.
At the preseot day it is nob so much dogmatiom, prejudice or a reckless spirit of speculationin men, that maintains rival theories in geology, as that higher metamorphic power of nalure which is ever reproducing tho elements of
38
Wo have seem that vor Buen refers these beds to contraction of the substance of the granite ata time when it had a degree of consistance »which in most cases was fur removed from the eancdition of fluidity.” But may not the internal structure of granite and other hypogene rocks be primarily due, not to the merely mechanical effect of contraction on cooling, bul to the original comitions of crystallization? Reversing the Neptunian theory of the deposition of the primary rocks from a state of chemical solution in a hot Quid ‘upon the upper surface of the carth's crust, may or rather must we not conceive them to have been gradually deposited on the under surface of the crust? We must suppose that crystallization did not at once extend throughout the whole of any mass of plutonic fluid, but commenced in a layer nearest the refrigerating surface of the superincumbent rocks, amd thence slowly extended by accretions from below. Dr. Lanowua says that o sudden crpansion im [reezing particularly con- spicuous in the erystallizalion of solids which shoot into prismatic forms. The process of crystallization in laboratories is for this reason frequently attended with the fracture of the vessels in which it is conducted, It may be taken os a general truth, to which however there may probably be some exceptions, that bodies which crystallize in, freezing undergg the sudden expansion here mentioned, and that bodies which do not erystallize in freezing for the most part suffer a sudden contraction” (1). A priori, therefore, it might be pre- dicated as probable that the granitic fluid, like water, expands on congelation. This pre- dication. s¢ems to. be verified by observed phenomena. If the granite contracted on crystalli- talion, the crystals formed at and near the surface of refrigeration would sink, the hot Nuid from below would constantly ascend to the aurface, and when the central heat of the earth was ¢o much lowered) as to allow the erystals to reach the centre of gravity in a solid state, a nucleus would there be formed which would gradually increase until the globe was solidi- lied from the centre to the circumference; or, at all events, mo permanent solidification would fake place until the temperature of the whole fluid was reduced to the point of eongelition (2). Under such conditions, if the globe were originally a homogeneous fluid,
matter in different shapes, ond which so often assimilates her most diverse process im tha phenomenn which re- wult from them. We may seal to isolate particular processos, seb the slawp of a name and o theory upon them and extend their exelusive dominion, bat atill tho ministers of nature work together and in harmony, or rolber in then the anity of the abeolate will still manifest iteclf. We term somes rocks plolonio and some volcanic, and preacatly wa ore foreed to say Lhot they pass by insensible gradations into each olher, As our koowledge eetends all thie will probably appear bat a play of words. Restraining speculation, we may consider if om established that the plutonic and voleanic reeks are lho produce of the same process; Uhal congelation and depesilion may alike cance (he atratified stracture; and thal by a chemical aclion, offen slight. igneous recka may, im silm, become omimilated to sedimentary, ond sedimentary roche may, ia sila, become ovsimilated to igneots. Obser- velion alone ean rocenatroct the bistory of any given rotk, ood determine the limila wilhin which tranemalations are effected in nolure.
()) Preatiea on Heat, po al,
(2) This appears in granite to be ebout the same as that of irom (De ca Becne’s Aeport p. 191) whieh in alate in the table appended to Dr. Lanosma's Treatise om Meat (po 405) to be 2IGST® FP. but which appears by the improved pyromoler of Professor Dastece to be only 2786" F. (Penny Cycplordia Ari, Freesing and melting Pointe.) Ut should be observed however thal granites vary recy greatly in fasibilily, Trappean rocks were found by Sir W. oe ca Beene to fuse al the same lemperalure with copper or 1006" F.
and granite be the constant result of the internal congelation of that fluid, ‘ho solid érwst could ever hawe been formed. Dut assuming the existence of the crust apart from ‘all theorica of ifs origin, and limiting our view to the great Jakes or oceans of fused rock beneath particular portions of the crust or otcupying great cavities inva solid globe, which are all that Mr, Leet will, recognise as necessary to explain plutonic and. voleanic plieno- mena, it is obvious that, until the temperature of the whole lake or ocean were recoced to that of incipient congelation, the upper layer would retain its heated fluid condition. Ifso, the igneous fluid would have time to penetrate fissares to great distances in the same way as that of trap. But granite veins are generally found to be short and sinuous, a circumstance which contradistinguishes them from dykes of trap, and which seems only expli- cable on the assumption that the injective tendency of the fluid was counteracted by its tendency to congeal at the surface from contact with the rocks above and to remain there in that state in consequence of its expanding or becoming less dense when it assumes the solid form (1). The phenomena which have been discussed in this paper disclose two structures in hypogene rocks, the lamigar, aud the globular passing into the euboidal. Now the first may be due, in the case of guem, simply to excess of mica or to this incombination with other causes which have been advyerted to. The second is clearly the original mode of crystallization, if the above views are correct, or if it be granted, without reference to them, that granite soli- difies from the surface downwards, In the upper layer of the granite fluid, nuclei are formed, which gradually enlarge till their mutual expansion prevents further increase, and the layer, bearing the form of ifs mould (2), is complete. This layer is the upper bed or stratum, of ihe granite, and others are successively formed beneath, each, of course, con- forming to that above it, The spheres not only when first formed, but during the long
(1) The granite veins of Cornwall! and Jecon seem to demonstrate that a crast must have been formed while tha granite beneath retained ite Muidily, for it net only senda veins into the alates bal is itself traversed by veise of ihe same kind of granite. These ore also sometimes continued in the alate above. (Da ta Bacun’s Keport
» M1, 2).
2 From the point of fusion of granite being rery high compared with volcanic rocks, ond, I presume, as high as that of any sedimentary rocks, it follows that so long as the temperature of granite is above that point, it will continue reducing the incumbent recka at the plaoe of contact inte ite own mubstance, and will only cease to de so when if ie on the point of ceasing to be o fluid, Hence, probably, the shape of the veins. They were Alled with granite when ite temperature was reduced to that of incipient congelalion and when the fluid bad, o008~ quently, become thick, They shew, as it wero, ite last efforts io its fluid state to melt into the rock abore it, Even where the granite fluid at a temperature above 2789° entered a atraight mechanical fissure or crack in any rock, it would immediately begin to melt the sides. Tho veins are Uherefore more pyrogenous than mechanical. Trappean fluid, om the olber band, might remain in o fluid atate long after ite heot was inadequate to melt the adjacent rocks. It might therefore be forced into fissures without altering their previous form, Trappean veins might thus be considered as generally mechanical granite, as generally dyrochemical, for the irregular distribution of chemical ingredients in a rock would affech the course ef granitic reine in it. From the great difference in the fusing point of granite and trap, it probably also resalis that the former is never found as an overlying rock, whereas the later from its retention of fluidity 700° lower in the thermometric scale, admits of being impelled through fissures and spread over the surface.
(2) See nole in appendix.
40
period in which their ingredients retain a viscid consistency, will, from the expansion con- sequent on crystallization, be exposed not only to mutual lateral pressure but to pressure from beneath, and. this will tend, according to the rate of refrigeration and other circum- stances, more or less to obscure or even obliterate the spherical form. Where there is a considerable proportion of mica the concentric laminar arrangement will still be preserved. 1 cannot follow out this view here; but the experiment on the gradual cooling of molten rock first made by Mr. Gaeconr Warr, and frequently repeated since, would seem to ex- plain all the gradations of igneous rocks. With reference to the hypogene rocks, ‘in order to conceive how the different species may be produced from igneous fluid beneath the earth's crust, we need only consider under what different conditions the fluid must have existed as to tranquillity, agitation, or motion, — the extent and form of refrigerating surfaces, — the nature, thickness, and pressure of the refrigerating masses themselves, whether rock, or sea, or both, — the rate of diminution of temperature, — and the propor- tions of chemical ingredients. Many of these conditions may have varied in different por- tions of the same great fluid mass, and at different stages in the process of its crystallixa- tion and solidification. The phenomena attending Mr. Wan's experiment even seem to shew that the globular, cuboidal, or prismatic concrefionary structure of micaceous granite might pass into the laminar gneissose structure merely through oscillations in temperature during solidification. An analogous passage from nodules into layers, and, in the latter, the arrangement of the crystals of one of two or more different minerals in continuous parallel laminae, characterises some volcanic rocks.
If expansion on crystallization be attributable to the nether hypogene fluid masses’, ond they are gradually solidified from above downwards, a slow upheaval of the superincumbent erust must attend their solidification when they are of sufficiently great extent. This may be the cause of the elevation of Scandinavia and other countries, at present in progress.
Whatever may be the origin of the bedded structure of the hypogene rocks, it is to a similar stratification, combined with the vertical joints, that the forms assumed by the ex- posed masses on “Pulao Ubin must probably be referred , and to these I now finally return.
The blocks protruding from the hills or ranged along the shores of Pulo Ubin are more solid and less decomposable masses and nuclei, of which the forms, and the directions of the sides and axes, have, in almost every instance, been determined by structural planes, and which remain after the surrounding rocks have disintegrated and been washed away, With respect to the latter, it is obvious that while the Island has been extending by the growth of alluvium in its bays, its more open const has been slowly retreating, so that what was once a part of the solid land is now a band on its border washed by the sea, but still exhibiting numerous rocky remnants. The larger masses still evidently occupy their original positions. Frequently their seaward face is curved. Sometimes another mass stands behind merely separated from that in front by a chasm whose sides are porallel. With respect to the decomposition of the rocks on the hills, the soil is entirely derived from this source with the exception of a very slight superficial mixture of vegetable matter, which in many places is absent. In general, however, the blocks that remain are decomposing with exceed- ing slowness, One exception I noticed in the NW.—SE. side of the rock described at
Al
p. 12. The laminae being inclined inwards, in disrupting by their own weight fall some feet in front of the base, where a long mound of, earth has consequently accumulated.
I have now only to revert fo the grooves. The circumstances attending them which any hypothesis of their origin must explain are these: their general prevalence; the existence , however, of exposed rocks devoid of them; their being commonly confined to the . sides facing the exteriour of the Island, although sometimes found on other and even on all sides of a rock; their great depth and regularity; their general coincidence with divisional lines; their conformity to the course of rain; and their antiquity. It is this last circumstance which, presenting at the outset a great difficulty, leads, on further consideration, to what I con- sider the teue explanation, That meteoric influences have been the great agents of erosion T have already suggested, But the antique; permanent, character which is impressed on the reat majority of the rocks, their vegetable coatings,, the hardness and sharpness of) the external edges of the. grooves, and the |absence of all indications of the process of excava- tion being at present in progress, prove that) the; rocks must ave existed under very diffe- rent conditions from ‘the: present, to enable atmospheric forces to. produce results of such magnitude. The considerations which have hitherto occupied us in the concluding portion of this paper appear to me to indicate what those conditions were, The composition ond structure of the cxtermal rocks, unveiled by the action of the sen on the beach, , shew zones of soft rock (1), rows of globular decomposing masses, and of harder. ferruginous spheroids ofe. susceptible of being detached, anda general tendency to perpendicu- lar division. If, therefore, we conceive the external layer of the, Island, when it, first became exposed) to decomposition ,.to have resembled in character the zone that has been laid open for our inspection along the beach, it is easy to comprehend how the wasting away of the more decomposable parts might at last leave exposed masses, including bamds of the less stubborn material already partially soflened or disentegrated underground, and that the action of the atmosphere and rain torrents would gradually excavate the more vic ing portion until the solid remnants exhibited their present shapes.
The grooved and striated rocks of Europe are by some geologists supposed to, have, ra caused by the action of the great and rapid waves called waves of translation. induced; by the pudden elevation of the sca bed and londed with detritus. Now although. in Singapore there is ample evidence of violent movements in the position in’ which we now find’ the stratified rocks (2), we cam hardly conceive the Pulo Ubin rocks to have been, subjected to
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(1) Some rothe may be seen along the bench wilh chaeme 2 or 3 feel wide, Ube aides being quite bard aod the bellom o soft decomposed aubslence. In anoh eases o gone of rock difloring in composition from that adjoin- ing has evidently been gradually decomposed and washed oul,
(2) The nearest point of which this displacement can be observed is in the vicinity of Singapore Town, abou! eleven miles to the south west of Pulo Uiim. But the whole intermediate country ia broken up in the same mao- ner, so os to present the appearance, in many places, of a tempestuous sea, and tho billowy hills are throughout so connected ond similar, that there can be no doubt thal tho forces which elevated them operaled during tho samo period over a wide area, including the southern portion of the Peninsufa ond ite outlying Archipelagoes. | This
ao" nee, 1847. F.
43
these movements since their consolidation. The first harried view of a portion of the masses at the quarries left the impression that the rocks had been shattered and separated by such forces. But I am now satisfied that, with some slight exceptions due fo decomposition and consequent alteration in the balance of the different parts of some of the larger rocks, they all occupy their original relative positions, and even their original absolute positions with reference to the horison, although the level of the whole Island and adjacent tract has probably shifted. At all events no violent vilbratory movement has affected the Island since the joints were formed and the mass stood above the surrounding tract. I cannot think that a wave of power adequate for the excavation of the channels could have been generated by a movement which would have left the projecting rocks undisturbed, or cven that the force of the wave itself could have met with such resistance from the smaller rocks as to enable it to grave the channels instead of displacing the rocks. No doubt a large proportion of these rocks were formerly firmly wedged into the mass of the Island, but many must have been more or less isolated, as the channels embrace more than one side, The undulations, ifany, attending the elevation of the Island and inducing waves of translation (if they were sufficiently violent, ond the upheavals sufficiently great) would probably be in the direction of the Peninsula; and, after the Island and the adjacent hills of Singapore and the mainland rose above the sea, waves might act on both sides of the Island transversely fo the line of undulation. But as the principal fissures and soft bands are in the same direction, the circumstance of the grooves mostly coinciding with it docs not ‘peculiarly fovour the application of the wave theory. But in rejecting its applicability, we may, at the same time, allow that the action of the waves, whether ordinary or extra- ordinary, as the Island gradually, or by abrupt steps, rose above the sea, may have as- sisted to a considerable degree both chemically and mechanically in wearing the channels. On the coast of Singapore opposite the eastern extremity of Pulo Ubin, and only a mile distant, there is a layer of pebbles evidently marking the last step in the elevation of the land. Such pebbles driven to and fro by the waves against the rocky beach of Pulo Ubin would be instrumental in deepening hollows.
Since a portion of this paper was written I have seen, in the nomber of the Quarterly Journal of the Geological Society of Zendon for May last, in the Presidents annual address to the Society, a notice of the observations made on the coasts of Sweden and /Vorway, last year, by M. Duaccnea. M. Dvnaocwea found along a portion of the coast, and par- ticularly im the Islands off it, deep channels and furrows in directions from NW. to SE., some 10 to 20 inches wide and 5 to 10 feet deep, oseffects of erosion,” saya the President, » on a much greater scale than I remember to have read of before.” The re- semblance of these channels to those of Pulo Ubin is not confined to their unusual size, but is carried out in the circumstance of the sides of the interiour of many of the channels being grooved in the directions of their longer axes, of their sometimes dividing into two
iract, [Fo have already ssid, is probably but o amall section of a vast region, embracing Jadia on the one side and duttralia on the olber in which similar forces were in aclivily during the same period, and produced similar effects.
AS
or more branches which afterwards re-unite into one, of many being rectilinear but many being undulating and bent in short waves, and lastly of the axes of the channels and the striac in their interiour having the same general direction as the depressions of the neigh- bouring country. Mr. Honsen refers to the Bulletin of the Geological Society of France (tome ITl p. 64) for some important views as to the causes of these phenomena. I have not access to the Bulletin, and cannot venture in my ignorance of the rocks and all other details, to make any further remarks on the analogy between the channels described by M. Dosocuea and those of Pulo Ubin; but it is probable that the structure of the rocks will be found in the one case ag in the other to have facilitated the erosion of the chan- pels, and partly given them their directions.
Singapore, sf, Oct. (846.
=a FE BF EE Se EEF EB Ee Note fo p. dd.
With reference to the views in the text if may be aaid that no em Fee could take place till the temperature of the whole moss woe of that of fusion, because until thon there would bo a constant interchange of level belween the successive upper or denser layers and the lower, Without resorting to the supposilion that gradual expansion as in water may begin prior to congelation, it seema clear that in such a dense fluid as molten gracite ander greab pressure, the passage of one portion through another muat be offected with difficulty and very slowly. Belweeo the level at which thé maximum temperature ceases, and the refrigeraling surface, there must, in such « fluid, be on insensible and very gradasl diminution of heat, and deep momes may be viewed of consisting of layers of considerable thickoees in any one of which the temperature ia almost uniform ond between which and the adjacent lsyere the transfer of heat is exceedingly slow. It may bo proper to examine thie further, because when the text wae written | overlooked tho chapter in Mir. Livers Prinaiples (Ch. XIX of Book Ul) in which he controverta the doctrine of the internal fluidity of the by an argument which is partially opposed to some of the above views, although it doesnot interfere with my general inferences. [ta object is to prove thal oo consolidation at the surface of a fluid masa like the globe could take place, till the whole had been reduced to o uniform heat or about that of incipient fusion, It appears (mote p. 440) thot M. Posse had, independently, adopled the sume argument, ood thal he imagined thal if the globe ever passed from ao liquid to o solid alate by-radintion of heal, the central nucleus mist have begun to cool and consolidate firel. The principal facta on which Mr. Livece relies are, that ao long as & fragment of ice remains in water the temperature of the waler, cannot be raiwed obove 32", and that Professdr Dassett found that while o solid pieeo of iron ele. remained immersed in o molien mass of the same aub- stance, its temperature could nol bo raised above the melling point, The remarks in the text relating to the ori- gin of granitic structure do nol require mo to assume that the lemperalare of o nilic mas wae ever much shove that of its melling point, o ir gen ah it should berecollected, higher by 700° (han thatal which basalt can exist in the fluid state; ond of Mr. Lrece does not seem to deny, with M. Porssox, the pousibilily of o crust being formed when the general temperature is near that of fusion, his remarke are nol Scnetabotial with the hypo- thesia thet granite has crystallized in successive Inverse. Eveo if the granile Moid approsched to the condilion of waler, instead of being comparalively very dense, the congelation of the firal layer would fend to maintain the fluidity of the next for some time, nol merely by arresting the interchange of particles by which ite beat had (hitherto been traneferred to the surface, ond substituting for it the process of conduclion, but yf? adding to it the large quantity of latent caloric expelled in the ach of congelalion, With reference, however, to Mr. Liete'’s ar- gumeot, i} may be remarked that the condilions to which a fragment of ice or iron are exposed when immersed in a finid mass of the same substance, and beat constantly added from a source close to it, are very different from those of n crust resling om tho eame fluid, in contact on one sido with o refrigeraling surface, ond on the olber with one to which calorie slowly necends from a seurce far below. The immeropd fragment is enveloped in o ra- a, heating mediam.~ The floating crost is belween two modin, one alowly giving heat, the olher abstracting it. he period, therefore, at whieh a crust can be formed is not determined simply by the fusing point (that is, ne- cesearily or wolil the whole mas hos reached ile lowest floid temperature) but ia determined by the relalira rates af which bent nsconds through the subslance in its floid stale, and is conducted from it when in ils solid state. The Intler is on indelerminate quantity, depending , na iLin some measure dees, upon the nature of the refri- geroling bedy. Bat, laying thal out of view, it is evident thol ow the bool diminishes, the rate of ile passage from one level te another will also decrees, because the motion of the particleaof the fluid amongst themeelves will be impeded os the density increases, Now long before the masse generally is reduced to tho temperature of fusion, the density of ile higher portion may renoh the point af which the rale of motion has subsided to that ob which heal is given off by a solid crust, Refrigeration may come lo ao atage at which, while the upper layers are ol and near the point of fusion, the lower may be far removed from it in proportion to the depth of the mass. Because in o receplacls of water exposed to a cold almosphere we see a rapid interchange of particles, ond the formation of ee puslzcar® Ci) all the lower layers have renched the temperature of about 40°, we are nol entilled to con- elude that in the successive layers of a deep abyss of dense mollen granite there will be a similar rapidity and extent of mutual motion of particles. Ewen in the caso supposed by Mr. Loar, of the globe consisting of walter having ol the ceotre a temperatare of 400° which gradually decrensed towards the cireumference where a crost ef ies fifty miles in thickoess existed, ia it necessary that we should admit wilh Mr, Lrece that the ice would aoon malt into an atmostphere of steam? In o Inver a mile in thickness the temperature would not increase one degree. At @ miles beneath the ice the temperature would be only 40°. Holow that the counter currents would first be encountered, but the rate of their motion in a layer a mile in thickness in which the summit only differed from the base by 1° would be so extremely alow as to be ingonsihle. Bot, to render the cases of a globe of water and a globe of granite more analogous, the globo of walter should bo supplied with a refrigerating oalmosphera at a temperalare more than 2600" below zero, for such is the differenee of lemperatare belween that of the almoaphere (even taking that of the equator) acd the fusing point of granite. With such a medium, or eren ono of which the demperatare waa calenlated according to the fusing point of trappean rocka. the heal giren off on the upper side of the fey erust might exceed that received from below even wilh a contral tomperalure of (400°.
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