Benson.—Structural Features of the Margin of Australasia. 109 
The main trend-lines of the later stage of mountain-making are now 
accurately known, and coincide approximately with the longer axes of the 
islands, while the deep-sea basins are found to be elongated arcuate 
synclines parallel to the adjoining rows of islands. The continuation of 
such movements is shown the frequency of earthquake-shocks along 
the trend-lines, while they are notably absent from the stable region of 
eastern Sumatra, northern Java, Borneo, and the southern China Sea. 
A very noteworthy feature is the obliquity of the modern geanticlinal 
axes to the strike of the Tertiary folds, which want of parallelism Brouwer 
explains by the supposition “ that the rows of uplifted and fragmented 
island-blocks indicate the places where at a greater depth folding continues, 
and that there is motion in a vertical direction as well as considerable 
motion in a horizontal one. The vertical movement will cause gradual 
erosion, and the exposed surface of the geanticline will in time consist of 
rocks which were in the zone of flow during an earlier stage of mountain- 
building. The rate and direction of the movement of the deeper-lying 
rom the rate and direction of motion of the rocks that lie at still 
greater depth.” 
Of noteworthy significance in connection with these movements is the 
distribution of the ancient and modern volcanic centres. During the recent 
rustal movements in the outer row of islands around the Banda Sea, 
. where the crust has been thickened as a result of overthrusting, the magma 
has not reached the earth’s surface, while the inner row, with a thinner crust, 
is characterized by a great number of volcanoes on the top of the geanti- 
clin Where the two rows are nearest to one another, just now at Timor, 
there are no active volcanoes on the inner row, and the voleanoes on this 
prevent the formation of ot “ We see in the inner row of islands 
of the south-eastern бернн an instance of extinction of volcanic 
activity on the top of the Bree € uring a renewal of the mountain- 
building process " (Brouwer, 1917).* 
* It may be permissible to cite a few more sentences from this work (pp. 803-4): 
** Tf tangential pressure reveals itself in the formation of normal folds the molten magma 
ill, under compression from all sides, force its way thr ас; = crust, with unequal 
strain first near the top of the anticlines where tension takes pla In the case 
isruption the tensio icli 
disa IS Or 
decreases, and the vents of эм volcanic magma leading to the surface, maintained by 
the tension, can gradually Ane up. Movements on a large e scale will give rise 
to overthrust sheets, [жена rc earth's crust in si ne addi- 
tional reason for the stopping-up of the volcanic vent. A new way is opened for the 
gma to reach the artic along the thrust-planes. Most often the magma, if it Seeger 
the surface, will appear on a lower level—i.e., in the region here discussed, below 
5 of the along the outer margin "die row of binds al movements i 
direction of the ‘ Vorland' will cause the rem ucts to be gra ually overlain 
by the moving masses." In discussing the o of the “green rocks" of the 
ving m ps 
and the older basic volcanic rocks of the Malay” ей е writer (Benson, 1924) 
the 8 
overthrust crust-flake above and the overridden submarine lavas ow, there may 
be псе those intimate associations of gabbro-peridotite and pillow- ba that form 
so noteworthy a feature in the Mesozoic rocks of Switzerland—e.g., in the Engadine— 
and in those of the Malay Archipelago 
