Have you ever wondered why Bukit Timah Hill is just that?

I mean, have you ever wondered why it's only a hill, and not a mountain? In fact, strictly speaking, the very name, 'Bukit Timah Hill', is tautological, because 'bukit' in Malay, means 'hill'. So, why is it 'Bukit Timah', and not 'Gunung Timah' ('gunung' being 'mountain' in Malay)? Second, why is it 'Bukit Timah Hill' and not just 'Bukit Timah'?

At a very basic level, it's 'Bukit Timah' and not 'Gunung Timah' because the landform at Timah is only 162.5 metres above sea-level [?]. To put this in perspective, Mount Everest, the tallest mountain in the world, is 8848 metres high. Thus the first question is answered, albeit at a very basic level.

The answer to the second question - why we refer to it as 'Bukit Timah Hill' and not 'Bukit Timah' - is far more abstract. Ask the question to the man in the street and he will tell you, quite rightly, that 'Bukit Timah Hill' is the name of a hill (in this case the highest natural landform in Singapore), whereas 'Bukit Timah' refers to an entire area, from Zhujiao Centre at Rochor, all the way north to Bukit Panjang.

An obvious case of a region [?] in Singapore, then? Indeed. Note how in this case, the region called 'Bukit Timah' has taken its name from a prominent physical landmark, and is defined more or less by the routes taken by a major road and an expressway (the Bukit Timah Expressway).

What is even more interesting is that there is a remarkably close correlation between the Bukit Timah region and the occurrence of a large band of granite (called a 'batholith' [?]), measuring eight kilometres north-to-south and seven kilometres east-to-west. The batholith is shown in light green in the diagram below.

There remains another question to be answered. That is, why is the granite there in the first place? In order to answer this question, we must first understand that the Earth's crust is divided into a system of continental and oceanic plates. The former are less dense because they comprise both granite (the average density of which is 2.8 g/cm³) and basalt (3.0 g/cm³), whereas the latter comprise only basalt.

Both granite and basalt are formed from the crystallization and solidification of molten rock (called 'magma') in the Earth's crust. Granite is a grey, medium-grained rock consisting of smoky quartz [?], pale yellow feldspar [?] and mica. Basalt, on the other hand, is a dark-coloured, fine-grained rock, with a high content of iron and magnesium.

The 'Virtually There' Geological Archives: Bukit Timah Granite - a 248 k QuickTime VR object.

The continental plates are moving with respect to each other, and because the planet is of a finite size, this implies that at any one time along the plate boundaries, the margins of the plates are either converging, diverging or moving alongside each other.

Singapore rides on the Eurasian plate, and this is less dense than the Indo-Australian plate which is converging against it. The great heat and pressure caused results in part of the Indo-Australian plate margin melting, releasing magma [?] which is forced up towards the crust.

Very near the destructive boundary, the magma has enough energy to melt its way right through the Earth's crust, till it emerges as the volcanic islands of Java and Sumatra. Further away (about 400 kilometres) from the convergence zone, where Singapore presently is, the magma had lost most of its energy by the time it got near the surface because it had started from very deep within the mantle.

As a result, the magma was unable to melt its way completely through the crust and instead cooled and solidified midway. That is, the magma was intruded into the crust. The crust bulged up, forming what we now know as Bukit Timah Hill. So now we know why Singapore will never experience any volcanic activity, at least in our lifetime, simply because we are too far away from all the action.

Many of you would, I'm sure, either have been to visit, or at least seen pictures of, Little Guilin Lake at Bukit Batok Town Park.

Little Guilin was formerly a quarry (now flooded) and is so named because the rocky scenery there resembles that at Guilin in China. The rocks there are known as Gombak Norite (shown in light purple in the geological map above). Norite is a variety of gabbro, which in turn is a dark, coarse-grained rock of basic (that is, non-acidic) composition, again formed from the intrusion of magma [?]. Norite has a high percentage of sodium and calcium feldspars, as well as dark green olivine. This is in contrast to the composition of granite, which is more acidic.

The minerals in the norite represent oceanic crust [?] trapped together with sediments from the margins of the continental plate during compression. Some geologists believe that the Gombak Norite is even older than the Bukit Timah Granite.

The 'Virtually There' Geological Archives: Gombak Norite - a 380 k QuickTime VR object.

There is a third group of rocks which were being formed at around this time. Continued uplift of the batholiths beneath the Main Range of Malaysia (otherwise known as the 'Banjaran Titiwangsa'), due to isostatic post-Flood compensation, increased the potential energy of the overlying rocks. Their rate of erosion thus increased, and the eroded material was deposited in shallow freshwater and coastal basins. Over the years, they were compressed into sedimentary rocks [?] called sandstones and mudstones, and in Singapore, they are termed the Jurong Formation.

The Jurong Formation consists of a wide variety of sedimentary rocks through the south, southwest and west of Singapore (shown in pink in the map above). Early studies of fossils from Mount Faber by Scrivenor (1926) confirm that the sandstones and mudstones were deposited in a low energy shallow marine shelf [?]. Generally speaking, however, well preserved fossils are rare in the Jurong Formation.

This might be because the basins in which the deposits accumulated were highly mobile. For instance, when uplift of the Banjaran Titiwangsa granites outpaced that of the granites along the east coast of Peninsular Malaysia, the basins were tilted and the Jurong Formation sediments slid eastward, resulting in complex folding.

An excellent example of such folding occurs at the extreme eastern end of St John's Island. In fact, the folds here are part of a whole sequence of distinct linear ridge forms found in the south and southwest of Singapore, from Jurong, through Kent Ridge, Mount Faber and Sentosa, finally terminating at St John's. The twists and turns of South Buona Vista Road (popularly known as 'the Gap' among the local racing fraternity) are another clear manifestation of the folds. Finally, however, the Singapore area had been elevated above sea-level [?] and sedimentation ceased.

The 'Virtually There' Geological Archives: Jurong Formation - a 330 k QuickTime VR object.

As our story continues towards the present day, the next group of rocks we come across is known as the Old Alluvium (shown in peach).

The Old Alluvium consists of sand, pebbles and gravel. The average thickness of the Old Alluvium is generally believed to be about fifty metres (Gupta et al, 1985). The deposits are believed to have been eroded from granitic rocks from south Johor. It was deposited when sea level in this part of the world fell, as the continents emerged from the waters of the Flood.

The 'Virtually There' Geological Archives: Old Alluvium - a 825 k QuickTime VR object.

As sea level [?] began to rise back to its present day level, the Straits of Johor were flooded and Singapore became an island. Even today, the Straits east of the Causeway are about twelve metres deep, while some parts of that west of the Causeway are as shallow as five metres! Two more rock formations were born. First, the Tekong Formation is a thin sequence of sands and gravels found around Pulau Tekong, Pulau Tekong Kecil, Pulau Ubin, Changi, along the northeast and southwest coasts, as well as in the tidal reaches of many of Singapore's rivers. It represents beach and offshore sedimentation as sea level rose.

The 'Virtually There' Geological Archives: Tekong Formation - a 429 k QuickTime VR object.

Second, the Kallang Formation consists of sands, silts, clays and peats found along most of the coastline and in the lower course of river valleys. These latter formations are shown in yellow in the geological map above.

The 'Virtually There' Geological Archives: the Kallang Formation - a 880 k QuickTime VR object.

That, in a nutshell, is the story of how Singapore came to be.