84
WILLIAM MACNAE
Such settlement a t the seaward end of a creek is prevented when
the time taken for settlement is longer than the slack of the water at
low tide.
I n areas where the uppermost intertidal levels are bare of vegetation
the deposits are often sandy. This is almost certainly the result of a
very short period of inundation, during which the tiny waves waft away
any fine material from amongst the sand grains and no time is available
for deposition.
Many mangrove areas result from accretion on recently submerged
coastlands. Obdeyn in several papers published between 1941 and
1944 has followed the history of the Sumatran, Javan and Malayan
coastlines from a study of Chinese, Indian and other historical records.
He has shown that during the early historical period Sumatra was still
joined to the mainland and to Java, and that the Malay Peninsula
extended southwards through the Riouw-Lingga archipelago almost as
far as the tin islands of Bangka and Billiton. The suggestion follows
that the silting up of estuaries in south-east Sumatra followed the
opening of the Straits and the subsequent development of backwaters
some distance from the tidal rips which run in t,he narrow channels
between the islands.
Such alterations of shore level are of twofold origin. I n Malaya and
the Sunda archipelago, change of sea-level is due both to eustatic
changes resulting from the Pleistocene Ice Ages and to epeirogenic
movements resulting from the processes of deformation and mountain
building which began in the Tertiary and still continue. India, Africa
and Australia have been affected by the former ; western Malaya and
the Sunda are mainly by the latter.
I n many of the niangals of Sarawak there occur odd little clumps of
terrestrial forest often only a few acres or less in extent. Anderson (in
conversation) has commented that the soils of these islands of terrestrial
forest suggest that they have not been derived by normal processes of
accretion. But their origin has not been investigated!
The Sunda Shelf extends far out into the South China Sea (see
Fig. 7 5 , p. 227). This shelf is of interest in relation to the spread of
several animals and plants and its eastern and southern margins
correspond to “ Wallace’s Line ”, the south-eastward limit of purely
Asiatic land animals. The Sahul Shelf connected Australia and New
Guinea and several islands between, and it forms the limit reached by
many purely Australian land animals. The Sofala Shelf off cent,ral
Mopambique is probably contemporaneous, as also is the shelf off
Queensland within the Great Barrier Reef.
All these processes, then, have made the shores of the Indian Ocean
WILLIAM MACNAE
Such settlement a t the seaward end of a creek is prevented when
the time taken for settlement is longer than the slack of the water at
low tide.
I n areas where the uppermost intertidal levels are bare of vegetation
the deposits are often sandy. This is almost certainly the result of a
very short period of inundation, during which the tiny waves waft away
any fine material from amongst the sand grains and no time is available
for deposition.
Many mangrove areas result from accretion on recently submerged
coastlands. Obdeyn in several papers published between 1941 and
1944 has followed the history of the Sumatran, Javan and Malayan
coastlines from a study of Chinese, Indian and other historical records.
He has shown that during the early historical period Sumatra was still
joined to the mainland and to Java, and that the Malay Peninsula
extended southwards through the Riouw-Lingga archipelago almost as
far as the tin islands of Bangka and Billiton. The suggestion follows
that the silting up of estuaries in south-east Sumatra followed the
opening of the Straits and the subsequent development of backwaters
some distance from the tidal rips which run in t,he narrow channels
between the islands.
Such alterations of shore level are of twofold origin. I n Malaya and
the Sunda archipelago, change of sea-level is due both to eustatic
changes resulting from the Pleistocene Ice Ages and to epeirogenic
movements resulting from the processes of deformation and mountain
building which began in the Tertiary and still continue. India, Africa
and Australia have been affected by the former ; western Malaya and
the Sunda are mainly by the latter.
I n many of the niangals of Sarawak there occur odd little clumps of
terrestrial forest often only a few acres or less in extent. Anderson (in
conversation) has commented that the soils of these islands of terrestrial
forest suggest that they have not been derived by normal processes of
accretion. But their origin has not been investigated!
The Sunda Shelf extends far out into the South China Sea (see
Fig. 7 5 , p. 227). This shelf is of interest in relation to the spread of
several animals and plants and its eastern and southern margins
correspond to “ Wallace’s Line ”, the south-eastward limit of purely
Asiatic land animals. The Sahul Shelf connected Australia and New
Guinea and several islands between, and it forms the limit reached by
many purely Australian land animals. The Sofala Shelf off cent,ral
Mopambique is probably contemporaneous, as also is the shelf off
Queensland within the Great Barrier Reef.
All these processes, then, have made the shores of the Indian Ocean