GeologicaIly, 1ndonesia is complex. 1st consists of groups of large and small islands, situated between the Asiatic and the Australian Continents, and extends from 60 N. lat. to 110 S. lat. and 950 to 1400
E. long. The Archipelago is a heterogeneous geosyncIinal area divided into two dissimilar regions. One, the northwestern region, has been stabIe sin ce Pleistocene times; it has a quiet, regular submarine relief which consists of two Continental Shelves of extensions of the beach below the sea-Ievel, caused by denudation and sedimentation. The Continental Shelves are the Sunda Shelf uniting Borneo, Sumatra and Java with the Malay Peninsuia, and the Sahul Shelf joining Australia, New Guinea and the Aru Islands. The second region, situated in the Southeast, is unstable; it has a considerably active submarine relief and comprises Celebes, the Moluccas and the eastern string of the Lesser Sunda islands. The small deep-sea basins and troughs east of Celebes are especially notable.