302 
Records of ike Geoloyical Survey of Lidia. 
[vOL. XI. 
Submerged Forest ox Bombay Island. Observations by G. E. Ormiston, Eesident 
Eiiijineer, Eonibaij Port Trust, dated 29th May 1878 (communioated by 
Government). 
The strata exposed in the excavation for the Prince’s Dock consist of the 
surface silt or black mud, which overlies to a depth of from 4 to 5 feet a dense 
blue clay of varying thickness (from 0 to 20 feet), but nearly level on top ; 
underneath this is found loam, raoorum', and rock ; the latter is very irregular 
on the surface, running at times into long narrow i-idges and masses of bouldera 
with soil between. The I’ock is soft, and consists mostly of indurated clay 
nodules imbedded in a hard matrix. Numbers of trees have been found (about 
200 up to date). Many had been overturned before being covered with the 
blue clay, but the roots were only partially torn out of tlie loam or moorum in 
which they gi'ew, others were standing ujjright with their roots deeply planted 
in their native soil. The standing ta'ces only extend to the surface of the blue 
clay, none penetrated the muddy silt above ; and for a foot or so below the level 
of the blue clay, the timber was riddled by the Teredo navalis, or a similarly 
destructive worm. Most of the other trees also shorved signs of this worm. One 
tree was found charred on one side for a short distance. The largest trunk found 
was 46 feet long and 4 feet 8 inches in girth; some of the timber is quite sound; 
it is of the colour of dark rose-wood, and with a straight grain. The level of 
the roots of these varied from low-water extreme spring tides to 12 feet under. 
This shows the laud to have subsided at least 30 feet, as the trees must have 
grown above high-water mark. 
Note. —Tins discovery of tvocs, in tlio .spot on wliich they grew, helow low-water mark in 
Bombay Island is cliieily remarkable, because it shews that, in recent or sub-recent times, depres¬ 
sion must hiive taken place in the immediate neighbourhood of ground which appears to have 
been raised. The Briiiec’s Bock is on the eastern or harbour side of Bombay Island, and the 
Esplaniido surrounding the fort on the wo.stern .side, not a mile away from the dock, is composed 
of the rook called littoral concrete by Br. Ihrist, a mass of shells, corals and sand cemented 
together by carbonate of Tunc. It is scarcely possible that the materials of which this rock 
eonsi.sts can have been accumulated at their prc.scnt elevation above the sea; in all probability 
they formed, when first deposited, a sand bank or beach not raised above high-water mark, and as 
it is difficult to understand how elevation and depression can have occurred simultaneously 
on different sides of so small an area as Bombay Island, it is probable that the whole area has 
imdcrgone elevation and depression alternately. If the elevation be the older movement, then the 
Esplanade must once have been several feet higher than it now is; if the depression is older, the 
trees at Prince’s Bock have been at a gi'e.ator depth beneath the sea than they now- are. The 
former is perhaps more probable. 
Tliat such alternate movements of elevation and depression have taken place in Bombay Island 
was shewn by Br. Buist- many years ago, though to a sinaller e.vtent th.an now appears pro¬ 
bable. At the same time, before the depth to which depression ha.s extended in this case can be 
estimated, it is ueces.sary to .ascertain what kinds of trees arc repiresonted. If they be such as 
grow on land, the deparcssion must have been grc.atcr than if they belong to such forms as Avi- 
vennia nr Uniyuiera, which grow some feet below liigh-wiiter mark. Tlie circumstance that the 
trees are bore<l by Teredo is in favour oi their having gi’owu in salt marsh, where these mollusca 
are pcculiiirly abundant. 
W. T. BLANEOEB. 
' A local term for decomposed rock. 
“ Transactions of the Bombay Geographical Society, Vol. X, p. 177, 1857. 
