158 COMPENDIUM OF GEOGRAPHY AND TRAVEL 
granite, from amid which rise the 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 
(5663 feet), and to the Dutch as Goudberg. From 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 
