Report on the vegetation of the Andaman Islands by Mr. S. Kurz, Curator of the Herbarium, Royal Botanical Gardens, Calcutta. 1866 Government Printing Office Calcutta. Section 8 describes Andaman subsidence evident in 1858/1866. The bulk of the thirty page report consists of lists of plants. I omit transcriptions of these and earlier sections irrelevant to neotectonics. Kurz was captured by convicts and abandoned, but the details of this episode are not given. This extract was taken from the copy (see pdf) given to the Geol. Surv. India by the Mr Anderson mentioned on the first line.

1. Appointment I was directed by Mr. T Anderson, Superintendent of the Royal Botanical Gardens, Calcutta, in accordance with letter No.. 1224 of the Government of India, dated 27th February last, to proceed on board Her majesty's steamer Prince Arthur to Port Blair, and to collect the material for a flora of the Andaman Islands and while doing this to ascertain the proportion which trees known to be valuable for their timber, bear the rest of the forest, and also to identify botanically all timber that might be shown to me by the local Authorities. I received also instructions to do all in my power to collect living plants and seeds for the Botanical Gardens, Calcutta.

2. Journal Accordingly I left Calcutta on the 2nd April 1866, and arrived on the 9th of the same month at the place of my subsequent explorations. Having placed myself in communication with Superintendent of Port Blair, I began my excursions on the 16th April, and explored subsequently nearly the whole of the forest tracts around Port Blair and most of the eastern coast from McPherson's Straits to Shoal Bay, as also a good part of the western coast as far as Island Bay before Port Campbell, and visited some of the Labyrinth Islands and Rutland.

On board of Her Majesty's Steamer Diana , which was placed at my disposal for a couple of days, I obtained an opportunity to proceed to the entrance of Middle Straits, when I explored both the coasts of South and Middle Andaman as far as the western entrance of the said Straits.

On the 11th May, however, when on the point of entering the interior of South Andaman from Escape Bay, I was seized by the Burmese convicts, whom the Supt. of Pt. Blair had given to assist me in my work, and was tied hand and foot on the ground. These and subsequent circumstances, which rendered the carrying out of my proposed excursions through the islands impracticable, obliged me to return on Her majesty's Steamer Feroze to Calcutta, where I arrived on the 20th July last.

The little sketch map (Appendix A) of South Andaman shows partially the parts visited by me, and also the large extent of coutry remaining still to be explored.

3. Unfavorable time of the deputation.......

4. Duration of deputation too short for full exploration........

5. Geological Features of South Andaman and Adjacent Islands*

The whole of S. Andaman and Rutland is a hilly country traversed by narrow and steep ridges of no great height, and encircled by a complete barrier reef, on which a line of breakers is foaming during the rise of the tide.

These dangerous reefs are formed chiefly from Caryphyllia, Madrepora, Porites, Meandria and other reef forming corals. Between high and low water mark there exists in some places a swampy mass formed by a large number of yellow and flesh colored carnous sponges, covering the coral reefs, and exhuding a disagreeable smell in the neighbourhood.

The principal ranges all run from south by west to north by east , thus somewhat in the direction of the lines of out-crop of the different strata. They are most developed along the eastern coasts, where they attain sometimes a height of 1200-1300 feet, sending out numerous spurs to the sea. Ford Peak on Rutland island may perhaps exceed 200 feet in elevation and the Saddle Mountain in North Andaman is rather more than 3000 feet high. Towards the western coasts they gradually become lower; and nowhere on that coast are higher ridges observed than from 200-300 feet elevation, bounding usually fertile valleys of comparatively large size. Some isolated hills, however, may be seen further inland, which I estimate to be between 500 and 600 feet high.

The whole surface appears to be intersected everywhere by numerous steep ravines, which open out in all directions, and cause great difficulty in penetrating to the interior parts of the islands, which, I suppose, in general at very low level.

The hills and ridges rise very precipitously along the sides towards the sea, commonly at an angle of about 43° to 45° and often at far more. On their sides , towards the interior, this angle is generally reduced to 20° or 25° but exceptions can be seen everywhere.

The geological formations of S. Andaman , as well as the southern parts of Middle Andaman, is, as Mr. W. Blanford , Dep. Supt. of the Geol. Surv. of Madras informed me, quite identical with those of the Arracan coast. (Footnote: For the determination of the rocks and other communications, I am indebted to Dr. Stolickza and W. Blanford, of the Geol. Survey of India).

Chloritic Rock.- A broad strip of an indurated chloritic rock, probably of some kind of greenstone or trap, pervades the interior from Mangrove Bay and Watering Cove northwards in the direction of the higher ranges of the eastern coast and reaches the eastern sea shores at Middle Andaman. The same rocks appear also on Termoklee Island (one of the Labyrinthe Islands), where they come into contact with coarsely stratified serpentine rock. This indurated rock appears to be rather felspathic , it is of greenish color, scarcely stratified, but intersected by veins of quartz and calcareous spar. Small cavities occasionally occur in the rock, exhibiting on the interior walls a large number of quartz crystals and other minerals. It is remarkable that, so far as my observations allow me to judge , this green rock appears to occupy the greater part of the level lands, but it does not form ridges or hills of any of any height worthy to be noted; but we know, in fact, nothing about the formation of the hills in the interior parts.

Sandstone.- The next rock, which covers a great area of South Andaman is a grey sandstone, dipping north by west with an angle of from 43 to 45°, or thereabouts. This sandstone is throughout of a very fine grain, showing a large proportion of silica, and occasionally being rather micaceous. The strata exhibit usually a distinct cubic structure, The rock itself decomposes easily, and forms in general a good clay soil.

Along the western coast of Port Mouat this rock is excavated and variously worked out by the sea , exhibiting there many fantastically formed rocks resembling in appearance the limestone rocks on the Mingan Islands.

Often, as for instance very finely on Bird island near Viper, this sandstone is interlaid in thin layers, colored rusty by oxide of iron.

Serpentine Rocks- Serpentine rocks are found chiefly to the south of Corbyn's cove in a south-western direction, and including nearly the whole eastern part of Rutland Island, (but also occurring on Ternoklee Island). This formation is easily traceable along the coast by the reddish color of the rocks , or by the brick colored soil, which originates from the decomposition. The strike and dip are in general the same as that of the grey sandstone.

At Birds-nest Cape, where these rocks attain a height of 70 ' or more, a cubic structure, similar to that of the common grey sandstone, can be observed.

The unaltered rock is mostly of deep green color, as impure serpentine rocks usually are . The stratified portion of the rock, however, which is much more decomposed, exhibits chiefly a reddish brown color, and is very ferruginous in some places. It would be, perhaps, worth smelting, but I saw no limestone at hand.

Behind Humphray's Ghaut, a narrow strip of serpentine is met with, which might also be usefully employed for practical purposes. It is tolerably pure and quite soft, so as easily to be cut with a knife.

At McPherson's Straits a dark green variety of serpentine rock, with dialage is see, not only in isolated rocks in the sea, but also on the low ridge of the coast,

Syenite:- A microcrystalline syenite has been traced near Watering Cover. It seems to be only of very limited extent, and surrounded everywhere by the indurated chloritic rock.

Conglomerates, formed of coarse pebbles of quartz, chloritic serpentine and sandstone, have been observed in large quantities at Muddy Creek, at Shoal Bay, and on Termoklee Island. They occur principally in the sea.

No fossils whatever have yet been observed on the Andaman Islands.

Barren island is an active volcano, about 50 miles distance from Port Blair and already too well known to need further remarks upon it.

Narcondam island has an extinct volcano remarkable for the great height of its cone, being twice as high as the outer wall. Owing to the great height of the cone (perhaps 2000 feet), in proportion to the surrounding wall, this island must have sunk very much, or the volcano must have been formed from a considerable depth in the sea.

6. The diversity of the soil.....

7. No veins of metals have been observed....

8. Probable sinking state of the Andaman Islands (footnote: In Darwin's map the Andamans are noted as "rising").

When approaching the Middle Straits from the south, a narrow reef can be observed (Barren Reef) at the entrance of the same, extending from the sea from South Andaman in a nearly easterly direction. This reef is covered with dead and bleached trees, variously damaged by the influence of storms and weather. The first impression is accordingly that all these trees have been destroyed by the influence of the north east monsoon. I observed, however the same phenomena along the whole length of the Straits, both on the reefs as well as in the mangrove swamps. Old trunks appeared from time to time in the sea, with their roots still attached to the ground. I find also the same phenomena was report of the Andaman Committee [Rec. Govt. India, XXV, Section 157]. This induced me to examine this peculiar feature more carefully, and I landed for this purpose at different places on both coasts of South and Middle Andaman. Some of the stumps of the trees proved to belong to such species as never grow in the mangrove swamps, nor in any locality such as that in which they are now standing. They appeared to me to belong to Pongamia, Erythrina , Thespesia and even stumps of Bruguiera pymnorrhiza were frequent, and of a larger size than which grow close to the shores, but apparently agreeing with those which are everywhere found further up the creeks. All these (except the last mentioned) are trees which never occur in the mangrove swamps, but in a sandy soil just behind them, or else bordering the sea where the shores are very steep and not adapted for the formation of mangrove swamps. This latter circumstance, however, cannot be the case here, the shores at the places where I made the observations being level for some thousand paces inland.

A more evident fact proving the sinking state of these islands can nowhere be seen more clearly than in these Straits. One can there trace in several places the stumps of the sunken trees in the sea up to the state where the trees are just dying by the influence of the sea water, and the subsequent change of the soil by the formation of the mangrove swamp.

The sinking state of the islands is further shown by another fact recorded in the report of the Andaman Committee, dated 1st January 1858, in Sections 8 and 9. There it is stated that the sea encroached some 40 or 50 feet since the first settlement at Catham Island in Port Cornwallis, so that the store house that stood there has been destroyed by the sea since the abandonment of the place in 1796. An examination of the spot and of the documents relating to that Settlement might give us some guide to determine the rapidity with which these Islands are becoming submerged.

Figure left is from the 1858 Andaman Committee report showing the abandoned store house remaining from 1796.

Lt. Jameson, of Catham Island, has informed that a similar encroachment of the sea is taking place [as] at that Island in Port Blair.

Andaman Straits which is impassable at low water for boats, will perhaps afford another good proof of this subsidence. I had no opportunity of visiting these Straits. McPherson 's Straits owing to its more abrupt coasts , does not exhibit this phenomenon , as far as I was enabled to ascertain. It is also a matter of great interest to decide the question whether the rapidity of the submersion takes place equally through the whole group of Islands or rather whether it is a decreasing one towards the northern extremities.

Dr. Mouat, in his able account of the Andaman Islands (selections from the Govt. of India, XXV) maintains quite a contrary view of this subject, as is shown in his preface where writing about the Andaman Islands he says-"They are collections of Islands surrounded by most dangerous coral reefs, which are gradually forming innumerable Islands as each becomes lifted above the surface," etc.

Dr. Von Liebid (in the same Records p. 127) points to a probable rising of Barren Island, recording thus "One of the most remarkable amongst these was a stratum of rounded stones, like large pebbles, cemented by tufa, exactly like those of the present beach, but at a considerable elevation (about 20 feet) above the high water mark, showing that the sub-marine base of the Island must have been raised since those pebbles had been washed by the sea".

Dr. Playfair (C. p 123), however , says -"I could not after very careful examination, satisfy myself that there had been any recent upheaval of the islands, none of the rocks exhibiting signs of having been water worn".

It may be remarked that Barren Island is an active volcano, therefore, probably rising and sinking.

From a practical point of view, the fact of a sinking state is of importance as we see all along the shores small fertile valleys opening toward the sea , and preparing themselves gradually for mangrove swamps.

Suppose the gradual submersion to be one foot in a hundred years (which is a rather low estimate) we should see in a thousand years all the shores and houses along the beach at Ross Island and Middle straits submerged while so many harbors now dangerous would become open for navigation.