256 THE GEOLOGY OF THE MALAY PENINSULA. 
Recent Deposits. 
They include many deposits of great economic value, such as: 
the ruby gravels of the Mogok Valley, and the alluvial tin-deposits 
of Burma, the Malay Peninsula, and the islands of Banka and 
Billiton. Where they are devoid of minerals they usually provide 
very good agricultural land, and the clay beds which thev contain 
are used for brick- making. In Borneo the old gravelly river-. 
depists generally contain gold, especially in west Borneo, but, 
although they are worked by the Chinese in certain rich spota, mat 
has not vet been proved that they are worth working on a large scale. 
In the Malay Peninsula it is fairly certain that the amount of gold 
in similar deposits does not pay to work by European methods. 
In the Malay Peninsula and in Sumatra there is evidence that 
the sea had a level, in recent times, higher than it has at present. 
In Sumatra it is indicated by raised sea-beaches, some more than 
300 feet above sea-level, and also by high gravel terraces in river- 
basins close to the present sea. shore. On the Peninsula, in Perlis, 
marine shells were found in a cave nearly 300 feet abor sea-level, 
but they may have been carried there by human agency. However, 
biological and geological evidence combined indicate that the Penin- 
sula was in Recent times connected to the Archipelago, so that 
Sumatra, Java, Borneo, and the Peninsula were united to form 
a continent. The sea level then rose until the Peninsula was a 
group of islands, and subsequent recession of the sea took place 
later which is believed to be still in Lee at the present day. 
Molengraaf does not agree that Borneo has been affected by this 
evcle. 
Under the heading of Recent deposits should be classed the 
deposits now being laid down by the active volcanoes in Sumatra, 
Java, and various islands. Barren Island, east of the Andaman: 
was last observed’ to be in eruption in 1789, and since then it has 
been dormant. In Borneo the Muller Mountains are built up of 
rhvolitic rocks, perhaps of Tertiary or of sub-Recent times, though 
it is also possible that thev may be so old as the Cretaceous period. 
It is interesting to observe that there is a close connection 
between the position of volcanoes, both active and recently extinct, 
and the lines of folding. 
