Dr. Tulley questioned how the very restricted occurrences of slump- 

 ing, as, for example, off the Columbia and Fraser Rivers, could give 

 rise to widespread effects. It was pointed out that material may, 

 however, travel long distances with steep gradients as at the bottom 

 of canyons. Dr. Emer}' mentioned a distance of 70 miles in fresh water 

 with a very low gradient. 



Dr. Tulley agreed that in the case of the Fraser Estuary mud might 

 be abnormally quickly precipitated owing to the high salt content of sea- 

 water. 



FORMATION OF THE SEA BOTTOM OF THE SUNDA SEA 

 By Dr. F. A. van Baren, University of Indonesia, Buitenzorg 



[A bstract] 



The Sunda Sea is the large shallow sea comprised of the South China' 

 Sea and the Java Sea situated between the Island of Borneo, the 

 peninsula of Malacca, and the Isles of Sumatra and Java. The minera- 

 logical research of bottom samples of the floor of this sea revealed that 

 ten sediment-petrological groups or provinces could be recognized, as 

 listed below, in their standard mineralogical composition. 



Standard Compositions 



Group. 



Transparent Minerals in Mutual Percentages. 



Krakatau — group . . 

 Y — province 

 Z — province 

 Deli — group 

 Bawean — group 

 Java — group, type I 

 Java — group, type II 

 Borneo — group, type I 

 Borneo — group, type 



n 



Meratus — Plant — 



group 

 Mixed province 

 S. China Sea — group 

 Malacca- — group 

 Banka — Billiton — 



group 



78 



The Krakatau- and Java-group, including Bawean and Deli-group, 

 are volcanic deposits originating from both recent and, especially in the 

 Java group. Tertiary tuffaceous sediments. They cover the southernmost 

 part of the sea-bottom of the Java Sea and of the Straits of ^lalacca. 

 They are characterized bj^ pyroxenes and/or amphiboles. 



The Y and Z provinces in the Krakatau area are of divergent com- 

 position. They are stratigraphically older and probably form the core 

 of an anticline on which the coral reefs in the Bay of Batavia and of the 

 Thousands Tslands are situated. The Z province ma}' be an old strand- 

 sand, as is concluded from the tvpical rounded habit of the garnet. 



218 



