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the almost perfect evenness of its bottom. This is the very sub- 
marine relief that would have originated, if this sea had been formed 
by the submersion of a large peneplain. The particularities of this 
relief may be explained assuming that this peneplain discharged 
its water towards the Bali Sea and the China Sea, and that a bay, 
from the present Sunda Strait encroached for some distance on it. 
For some hundreds of kilometers landward the surface of 
Borneo is only slightly undulating and the same is the case in the 
coastal region of Eastern Sumatra and on the islands in the Sunda Sea, 
as Bangka, Billiton, Singkep ete. The greater part of all this land 
partakes of the character of a peneplain *), rising only little above 
the sea-level, here and there with some gently sloping hills, consisting 
of rocks, which possess a more powerful resistance against erosion, 
emerging from the lower territory. This description applies less to the 
coastal fringe of Java, on which island voleanic activity repeatedly 
modified its sculpture and raised its level. 
The slightly undulating floor of the Sunda Sea is continued, as it 
were, on the surrounding land. Along the coast of West-Borneo a 
retreat of tbe sea to a depth of no more than 10 fathoms would 
join numerous islands to the coast and enlarge the still existing 
peneplain of West-Borneo with its peculiar, gently sloping monad- 
nocks, without affording any feature in the landscape to enable us 
to tell the old land from the new. 
All the islands in the Sunda Sea, as e.g. Billiton and Singkep, 
present so clearly the type of regions which on account of the existence 
of cores of hard resisting rocks were less subject to erosion than 
their surroundings, that spontaneously the idea forces itself upon us 
to join West-Borneo to Bangka, Billiton, ete., and to consider the 
whole tract of the Sunda Sea as a submerged peneplain, from which 
the present islands rose up as monadnocks, when in the pleistocene 
age the sea-level was lower. 
b. Character of the bottom’ of the Sunda Sea. 
The floor of the Sunda Sea about which little is known, appears 
„to be very muddy; the large majority of the soundings, performed 
in this sea, show that the bottom consists of silt or mud, whereas 
shells or coral-fragments are rarely reported. This can hardly be 
accounted for in a shallow sea like the Sunda Sea, by the influence 
of the rivers flowing into it now. Indeed, they transport a large 
amount of silt to that sea to a large distance from the coast, but 
1) Strictly speaking all that territory makes up that portion of the large pleisto- 
cene peneplain which has not yet been overflowed by the sea. 
