AN© GEOLOGY OF THE MALAY PENINSULA. I3T 
carried away. If in the present day, when the more exposed strata have 
been probably long since stript off the higher mountains, when the 
volcanoes have ceased to feed the channels of the mountain streams 
and rain courses with sand, ashes and tufaceous matter, and the less 
elevated stratified hills and slopes are densely clothed with vegetation, 
we are struck by the great accumulation of alluvion going on along the 
whole east coast of Sumatra,* how vast must have been the amount 
of matter poured down from the hare and easily abraded heights in 
the rainy seasons of the first ages of the Island. Broad as the east¬ 
ern plains are, it does not appear necessary to refer either their 
formation or elevation to other than merely alluvial causes, more 
especially as the breadth of the different basins of the great rivers 
seems to be in some degree proportioned to their respective magni¬ 
tude. All the facts hitherto recorded are consistent with a strictly 
alluvial origin. 
The course of the Jambi, for instance, has been accurately surveyed 
from the mouth of the northern and western branch, the Kwalla Ni'or, 
to the town of Jambi, which is distant in a direct line from the 
mouth of the main branch nearly 60 miles, but much more following 
the windings of the river. The water flows up as far as Ukam 
which is about 40 miles in a straight line, but the tide retards the 
stream and produces a rise of two feet at Jambi, and this although 
there is no estuary at the month to cause a high wave to rush up the 
river, and the force of the littoral tides is broken by Tanjong Bon. 
The channel increases in depth from the mouth,—where it is 16 
feet and the banks are only a little above the level of the sea at low 
water and consequently uninhabitable,—to J&mbi, where it is about. 40 
feet deep, and the banks 20 feet above the ordinary level of the river. 
It is at some places below Jambi nearly 100 feet deep. In the rai¬ 
ny season it rises from 12 to 15 feet, and at Miiara Jambi overflows 
The large islands of P. Rupat, P. BankSlis, P. Padang, P. Panjore and 
"P. Rantau, facing the Peninsular coast from Tanjong Tuan to T. Burn, are 
all alluvial, and appear to be great flats of mud formed by the sediment 
brought down by the Rakao, Siak and Kttmp&r. Extensive flats not yet rais¬ 
ed to the level of the sea extend in front of the four last islands. About one 
ball ot the present breadth of the Strait is occupied by these islands and 
banks. 
