158 COMPEXDIUM OF GEOGRAPHY AND TRAVEL 



granite, from amid which rise tlie peaks of volcanoes, 

 both active and extinct. Carboniferous limestones and 

 marls occur freely, but rocks of the Secondary Period 

 are conspicuously absent. It is otherwise with the 

 Tertiary formation, which is strongly developed. The 

 coal-measures, which are recent, appear to be very 

 extensive. 



The central mountainous ridge, the general name 

 for which is Barisan or the " Chain," consists in the 

 broadest parts of the island of more than one crest, the 

 intervening plateaux, lakes, or valleys, and secondary 

 connecting ranges. The nearness of this chain of 

 mountains to the west coast causes the larger part 

 of the drainage to find its way to the Straits of Malacca 

 and the Java Sea, and hence the detritus from the 

 mountains has been for ages forming the great alluvial 

 belt which extends along the whole of the eastern side, 

 and silting up the straits. The island, in point of fact, 

 is slowly but surely altering its position, and gaining 

 steadily to the eastward, so that the time is, geologically 

 speaking, not far distant when it will have reunited itself 

 to the mainland from which it has so long been separated. 



The two islands at the north end of Sumatra, Pulo 

 Bras and Pulo Wai, familiar to all who navigate the 

 Straits of Malacca, are in reality the commencement 

 of the chain just mentioned. The first peak upon the 

 mainland itself lies at no great distance from Ache, and 

 is known to the natives as Selawa-jantan or Yamura 

 (56G3 feet), and to the Dutch as Goudberg. Prom here 

 a secondary range runs eastward to Diamond Cape, but 

 the mountains are of no great height, and not comparable 

 in grandeur to Mounts Abong-abong and Luse to the 

 south. These volcanoes, being in the territory of the 

 hostile Achenese, have never yet been ascended, but their 



