THE MALAYAN AKCHIPELAGO. 87 



We next come to the Siinda Strait, where the island of 

 Krakatoa made a sudden explosion in 1883. 



JavaJ^ 



Although the large island of Java formed a part of Sumatra 

 at the end of the Miocene period, it differs from its western 

 neighbour in being built up mainly of the Young Tertiary. 

 Palaeozoic and still older complexes are only found in the island 

 of Karimon Java, off the northern coast, while Cretaceous and 

 Eocene beds occur in insular patches within the Tertiary upland 

 that constitutes the central axis of the island ; the south coast 

 consists mainly of Younger Miocene rocks, while the north is an 

 alluvial plain. Petroleum-wells are located mainly on the line 

 between Samarang and Eembang on the north coast in Miocene 

 beds. 



Java owes its special topographic relief not to the sedi- 

 mentary but to volcanic formations. The enormous masses of 

 extravasation and the vents of volcanic activity are arranged 

 linearly and correspond to the longest extension and the central 

 axis of the island. East Java possesses a double series of longi- 

 tudinal fissures in its crust crowned with mighty cones, one 

 among them being the active volcano, Semeru, which is the 

 highest elevation in the whole island, being 3,676 metres above 

 sea-level. The two chains converge at the narrow, middle por- 

 tion of the island with the extinct Penususpan and Slamat at 

 their junction. Their conjoined, and single fissure extends 

 through occidental Java to the well-known Krakatoa, and thence 

 to Sumatra, traversing by the way three volcanic districts, where 



7) Verbeek et Feuuema, ' Description Géulogic^ue de Java et Madoura,' iS'Jö. 



