62 
Mora of Narcondam and JBarren Island. 
of two—a western tertiary ridge most marked in the north and tailing 
off towards the south, and an eastern volcanic ridge most marked in the 
south and dwindling into insignificance northwards. 
The question whether the line in which Narcondam, Barren Island, 
and Flat Rock are situated consists of a series of isolated peaks, or if 
these peaks are only the sub-aerial portions of a continuous ridge, remains 
to be considered. Such evidence as there is appears to indicate that 
they are situated on a ridge : it is not, however, at all complete. It has 
already been remarked that the soundings on a line passing north-north¬ 
east from Narcondam are relatively shallower than those on any other 
line. This has been explained by Carpenter as perhaps indicating that 
the deltaic shelf of the Irrawady extends as far out as Narcondam.* 
It may be anticipated that this will not be found a sufficient explana¬ 
tion of the phenomenon. It will be observed that the soundings gradu¬ 
ally deepen for a space of 9| miles, till the bottom carries 362 fathoms, 
and that beyond this point it gradually shallows till the coast of Pegu 
is reached. If Narcondam were situated on the edge of a delta-shelf, 
one would expect that the soundings would not show so great a dip within 
its margin, and would further expect that soundings on lines carried at 
right angles to the line under discussion would give some indication of 
a more or less level area. Yet what we do find is that, before four miles 
to the east or three miles to the west of the island have been reached, 
greater depths have been obtained than the deepest sounding on the 
north-north-east line. This appears to indicate that Narcondam is not 
so much on the edge of a shelf, as at the end of a ridge that runs towards 
and into the Pegu coast-line. That this ridge is overlaid by the deltaic 
mud to within ten miles of Narcondam, and that the presence of this 
mud explains the gentle slope from its deepest point upwards to the 
Pegu coast is no doubt true; but the steady rise during the last ten 
miles towards Narcondam, coupled with the more abrupt dips to the 
east and to the west, indicate the existence of a ridge. The matter is 
capable of direct demonstration : a few lines of deep-sea soundings co¬ 
ordinate to the line of soundings taken towards the north-north-east, 
will disclose the true state of matters. It would also be equally easy, 
by making a line of borings along the continuation of its line, and a few 
co-ordinate lines across in the mud of the Irrawady delta, to demonstrate 
whether the supposed ridge passes subterraneously into Burma. 
The same comparative shallowness is indicated by the line of 
soundings to the south-south-west of Barren Island, and to explain the 
fact Malletf suggests the possibility of eruptions of ash distributed 
* Carpenter : Records of the Geol. Survey of India, xxi., 48. 
t Mallet : Records of the Geol. Survey of India, xxi., 47. 
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