58 
Flora o/Narcondam and Barren Island. 
through the rock; along this line the soundings show a rather sharp 
ridge with relatively shallower soundings for the whole length of 
the hank; this line, it is hardly necessary to repeat, is that on which 
both ISTarcondam and Barren Island also show their shallowest sound¬ 
ings, while the axes of all three islands indicated hy this direction form 
very nearly a continuous straight line. 
The nature of the bottom on this bank is only mentioned in the case 
of one sounding; this depth, 25 fathoms, gives, as might be expected, 
coral; it would be interesting to ascertain whether the subaerial portion, 
Flat Rock itself, is part of a raised coral reef, or a remnant of an origin¬ 
ally larger island of volcanic structure. Raised coral reefs occur in the 
Andamans to the west, and in the ISTicobars to the south ; it may there¬ 
fore be anticipated that here it will be found that the subaerial portion 
of the bank is weathered coral; at the same time it would be more satis¬ 
factory to have the question settled by a visit to the rock. Reasoning 
from analogy, however, there is little doubt that the basis of this coral 
bank is a submarine volcanic peak, and that it forms but one of a series 
to which the others also belong. 
Our knowledge of the bottom-contour of the Andaman Sea is not 
so satisfactory as is that of the Sea of Bengal. English geographers 
e:ive no attention to the point; German geographers have mapped the 
sea somewhat hastily and from rather meagre data. Thus Berghaus 
indicates by the contour lines in a map of “Heights and Depths”* 
that a deep gap, connecting the Sea of Bengal and the Andaman Sea, 
exists between Achin Head in Sumatra and the Mcobars. It has how¬ 
ever long been known that the ridge in this channel carries only 760 
fathoms of water. In a larger map f Berghaus shows deep water as 
overlying not only the ridge between the Hicobars and Sumatra, but 
also over that between the Andamans and ISTicobars and, what is quite 
unaccountable, between Preparis and the Coco Group ; this last channel 
has long been known to carry no more than 150 fathoms. As regards 
that between Little Andaman and the ISTicobars, Carpenter had, on 
grounds of temperature, predicted what Hoskyn has since shown to be 
true, that the ridge under it could carry at the utmost 740 fathoms ; its 
actual depth is 736 fathoms. In this map also two soundings are shown 
in the meridian of Lon. 96° 10' E., one of them in Lat. 11° 35' H., for 
* Stieler’s Hand Atlas, Sheet 8, dated 1878. 
t Stieler’s Hand Atlas, Sheet 67, dated 1881 and revised to 1884; scale 1: 
12,500,000. Perhaps the contour line in this map means the 100 fathom line ; this 
would explain the shading in the straits mentioned. If so, it is too far from land, 
and coincides with the 1000 fathom line rather than the 100 fathom one. 
272 
