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pened in reality. The ice-age has not been one single cold period, 
but a succession of colder glacial periods alternating with milder 
interglacial periods. Consequently the ice-caps more than once have 
grown to a large extent and have melted again. Thus we may sur- 
mise that during the first glacial period the Sunda-peneplain, which 
probably already pre-existed in an imperfect state, has recommenced 
to develop, that it has been covered by the sea during the first 
interglacial period, that during the second glacial time it was ren- 
dered more perfect, that it was flooded again during the second 
interglacial time and so on, until the last glacial period saw the 
peneplain in such a state of perfection as is now illustrated by the 
floor of the Sunda shelf-sea. 
Many pecularities of the Sunda Sea and its surrounding coasts are 
in keeping with this conception or are sufficiently explained by it. 
However, before dwelling on these peculiarities the following two 
questions must be answered: 
1. how far did the pleistoeene Sunda Land extend? and 2. what 
were its boundaries ? 
The Pleistocene Sunda Land. 
There is one answer for these two questions: the Sunda Land 
is that portion of the western half of the Hast-Indian Archipelago 
which emerged from the sea during the maxima of glaciation in the 
pleistocene age. We take this Sunda Land to have been covered 
gradually by the sea to a depth of 72 m. from the last maximum 
up to the present day. 
The Sunda Land consisted of Java and Madura, Sumatra, Borneo, 
Malacca, and the present sea with its islands round these countries 
to a depth of 40 fathoms (72 m.) as is represented on the map (Fig. 1). 
All that has been said, however, applies only to that part of the 
Sunda Land which has been stable or orogenetically inactive since 
the Pleistocene. The present isobath of 40 fathoms during the last 
maximum of glaciationin the pleistocene age, gives the ancient coast- 
line for that part. In order to ascertain the extent of the stable conti- 
nental part of the Sunda Land it is, therefore, required to know as well 
the boundary between the land that has been orogenetically inactive 
since the close of the Pliocene, and the land that has been active. On 
the sketch-map this boundary has been indicated tentatively by an 
interrupted line. What lies within this line is the stable part of 
Sunda Land, to be ealled Sunda-iand proper. 
To this stable Sunda Land belongs in the first place the entire 
