102 Transactions. 
sandy claystones and lignites. Very important crust-warping and block- 
aulting occurred in Upper Pliocene times, which determined the form 
and position of the present coast-line, .the raised coral-reefs, the main 
graben river-valleys, and many minor topographic features. The most 
marked of these graben extends almost throughout the length of Sumatra, 
and is separated by a relatively narrow range from the south-western 
coast. These latest structural lines often cross obliquely the older anti- 
extensive Pleistocene sediments; but Van Es considers it was in progress 
during and after the Tertiary times.* It is more marked in the older 
central geanticlinal portion than in the younger flanking sediments, the 
steeper dip of the southerly-dipping beds indicating the southward (out- 
ward) direction of superficial thrust. The periods of greatest movement 
- appear to him to have been in Miocene and post-Tertiary times. Ву the 
latter, Pleistocene coral-reefs have been raised as high as 2,500 ft., and th 
maximum uplift occurs where the Tertiary folding is most marked, the 
parallelism in location and direction being such as to indicate the inter- 
mittent action of a single group of forces of long duration. The outermost 
of the geanticlines is seen in the long submarine ridge rising to a depth 
of less than 1,000 fathoms, and separating an off-shore synclinal trough 
1,500-2,000 fathoms deep from the foredeep over 3,000 fathoms deep. 
Continued to the west of Sumatra, however, this outermost geanticline 
rises above the surface to form a string of islands including the Mentawei 
Group. As in Sumatra, so in Java, longitudinal, transverse, and diagonal 
fracturing was accompanied by block-faulting and volcanic eruptions at 
various times from middle Tertiary to the present date, and was instru- 
mental in determining the present topography. 
East of Java the main geanticlinal axis, with the volcanoes thereon, no 
longer forms a gently accentuated ridge marginal to a partially submerged 
plateau with the deep sea on one side only, but instead is a high and 
narrow ridge rising from considerable depths and broken by cross-fractures. 
It runs through Bali, Lombok, Sumbawa, Flores, and that string of 
islands, from Dammer to Banda and Gunong Api, forming the innermost 
of a series of discontinuous arcuate ridges separated by similarly inter- 
rupted troughs. The structure of this arc is not very clearly known, but, 
* Martin (1919) states, however, that the recognition of the various subdivisions of 
the Tertiary rocks in Java has rarely been based on palacontologically satisfactory 
ati 
are only exceptionally known. He therefore counsels caution in the acceptance of such 
ese. 
olengraaff (1922) suggests that another anticlinal ridge existed still farther to 
ich has since subsi isostatically into the depths of the Indian 
Ocean, leaving Christmas Island as its sole ntative above sea-leve Andrews 
(1900) has shown that this remnant consists of volcanic rocks and littoral calcareous 
formations, coral-reefs, &c., ranging in age from Oligocene to Recent. 
