102 
SKETCH OP TIIE PHYSICAL geoghaphy 
rectilinear, and in irregular variously curved planes. The partial 
decomposition of such rocks has produced, in the masses that are 
left protruding, the most singular and imposing forms. Amidst the 
luxuriant forest that always covers granitic hills and mountains, the 
explorer suddenly finds himself facing a high perpendicular wall of 
rock, indented by numerous vertical grooves sometimes 5 or 6 feet in 
depth. Very fine arid varied examples of these occur on the island 
of Pulo IJbin near the south east angle of Singapore. We have ob¬ 
served them also on Gunong Tunyo Laut, in the north east of Jo- 
hore, and, in a less regular form, at other places. 
In concluding this brief notice of the plutonic rocks we may ad¬ 
vert to the existence of several thermal springs in the interior of 
Malacca as affording an evidence that, at subterranean levels, the in¬ 
tumescence which produced the Peninsula has not yet parted with its 
heat. This, combined with some proofs of recent upheaval, that will 
be mentioned afterwards, leads to the surmise that it still retains the 
character of a rising region; a surmise which its proximity to Suma¬ 
tra countenances. 
Metals _The tendency to the production of metalliferous ores at 
and near the junction of plutonic and sedimentary rocks which has been 
observed in many countries, might have led us to anticipate a large 
share of metallic riches for the Peninsula. In reality it probably 
abounds in some ores far beyond conception. 
Iron ores are every where found, and in the south they exist in 
vast profusion. In some places the strata have been completely sa¬ 
turated with iron, and here the bare surface of the ground, strewed 
with blackish scoriform gravel and blocks, presents a strange con¬ 
trast to the exuberant vegetation of surrounding tracts, appearing as 
if it had been burned and blasted by subterranean fires. Much of 
the ordinary forms of ironmasked rocks, which are so common and 
so little regarded for their metallic contents that in Singapore they 
are used to macadamize the roads, contain often nearly 60 per cent 
of pure metal. 
The whole length and breadth of the Peninsula, there can be little 
doubt, abounds in Tin ore. The uuifprinity, we might almost say uni- 
