JOURNAL

OF THE

ASIATIC SOCIETY.

No. I. 1860.

Account of a Visit to Barren Island in March 1858. By G. VON LIEBIG, M. D.*

Barren Island is a volcanic island, situated in Lat. 12° 17' N. and in Long. 95°54′ E. Its smallest distance from the Andaman Archipelago is in a straight line only 36 miles East. The distance from the nearest point of the main land, near Tavoy, is about 270 miles W. S. W. It lies not far out of the straight course between Port Blair and Amherst, about 63 miles from the former, and 330 from the latter place. The Semiramis approached the island on the morning of the 19th March, 1858, coming from the N. E., and steamed round it by S. keeping close to the shore, until the ship was opposite the entrance of the crater (Fig. 2.) bearing about W. and by N. from the centre of the island, where she hove to, and we landed.

It is stated in former accounts, that all round the island the lead finds no bottom at 150 fathoms, only mile distance from the shore. Captain Campbell found however ground at that distance on one side. of the island, its centre bearing N. E. at a depth varying from 4 to 14 fathoms.

Nearing the island from the North and passing round to the South East of it, it looks from a distance like an oval-topped hill; but coming closer, the sides of the mountain are discovered to belong to a steep circular elevation, sending out spurs towards the sea and enclosing a central valley. The sides of the enclosing circle being low

* An account of a previous visit to this Island by Dr. G. R. Playfair, Bengal army, will be found in the 25th No. of the records of the Government of India. No. CII.-NEW SERIES, VOL. XXX.

B

er in the direction of the spectator, the upper circumference of this valley is seen in the shape of an oval ring, formed by the crest of the surrounding ridge. In the middle of this ring, the upper part of a regular cone is visible, from the apex of which small white vapourlike clouds emanate. It is also distinguished from the surrounding darker masses by its grey colour, and some large white marks on it, like fields of snow. An entrance is not discernible.

The slopes towards the sea are generally covered with shrubby vegetation, presenting however some bare patches towards the upper edge; small trees grow about the base, where large rounded stones are washed by the sea.

Turning now to the S. and S. W. the enclosing wall is higher than the cone and the crest of the opposite ridge, and both therefore disappear from the view. On this side the vegetation down the spurs to the sea may be called rich, and consists of different forest trees of moderate height, interspersed with graceful palms; and where the descent is rocky, the rocks are frequently covered with ferns.

Passing to the westward of the centre of the island, and continuing the survey towards the northern end, one of the first turns discovers a large gap in the circular wall, extending quite down to the base of the island, through which the interior of the valley, with the cone in the middle, opens at once into full view.

The sides of this gap or fissure in the circular wall form a regular cut or short transverse valley through it, opening towards the sea into a small bay, and on the other side into the circular valley, to which it is the only way of access. Opposite this entrance, in the centre of the valley, rises the cone of grey ashes, and surrounding its base the bottom of the valley is filled with black masses of cold lava, which are continued like a congealed stream through the gap, breaking off abruptly when they arrive near the water's-edge. At its termination the steam is about 10 or 15 feet high, and its breadth seems less than farther up. It looks like a black perpendicular wall drawn across the entrance and facing the sea.

The lava consists of a black basalt mass (matrix) throughout which are disseminated innumerable semi-transparent little crystals of a variety of common felspar (orthoclase), and also many bright green granules of olivine. The lower part of its thickness is homogeneous,

with a smooth fracture, but from the upper surface to a depth of several feet it is cleft in all directions, whereby the upper part is divided into rough blocks, possessing a spongy texture as well as countless sharp edges and corners.

The older lava, composing the rocks on the side of the valley and also the strata of the surrounding ridge is slighty different from this. The colour of its principal mass is a reddish grey, felspar and olivine crystals are embedded in it in the same proportions as before, and in addition small pieces of black augite of the granular kind, with conchoidal fracture. From underneath the black lava, where it terminates near the sea, issues a broad but thin sheet of hot water, mixing with the sea water between the pebbles of the beach. The Thermometer I had with me was not graduated high enough to measure its temperature, its highest mark being 104° F. (40° C.) The water where escaping from the rock must have been nearly at the boiling point, judging from the heat felt when the hands were dipped into it, or when the hot stones were touched. When bathing, we found the sea water warm for many yards from the entrance of the hot spring and to a depth of more than 8 feet. It is not impossible that a jet of hot steam or water may emerge from the rocks below the level of the sea. The hot water tasted quite fresh, and not saline as might have been expected, showing that it could not have been long in contact with the rocks.

We ascended to the base of the cone, passing along the sloping sides of the transverse valley through dry grass and brushwood or over sandy ridges, so long as the solidified stream of lava in the middle left us room to do so. At last we had to ascend the rugged surface of the black lava itself, and cross the circular valley, which has about the same breadth as the transverse valley (not quite one-eighth of a mile), until we arrived at the base about half a mile from the sea. The cone rises from the lava accumulated in the circular valley, and its base is about 50 feet higher than the level of the sea, at a rough estimate. It is quite round and smooth, and the inclination of its sides is 40 degrees. No vegetation of any kind was visible along its surface. We turned to the left and went up from the north side, where the appearance of a ravine, some way up, only two or three feet deep and very narrow with some tufts of grass growing along it, promised an

easier ascent for a part of the way, and where a rocky shoulder at about two-thirds of the height would offer a place to rest. Our ascent commenced at about 2 P. M., and was certainly the most fatiguing expedition many of us remember ever to have undertaken. The sky was almost cloudless, and the heat consequently was great. The lower third and more of the slope consisted of a powder of ashes into which we sunk ankle-deep, and we often fell a step back for two gained. A little higher, stones loosening when the foot stepped on them and rolling down in long jumps, were dangerous to any one following.

Arrived at the rocks mentioned, their nature and the manner in which the side of the cone bulged out in their neighbourhood, showed that they marked the point from whence an effusion of lava of the same kind, as we has seen below, had taken place from the side of the cone, not reaching the mouth of the tube at the apex. The last third of the way from the rocks upwards offered a firmer footing, the ashes being cemented by sulphate of lime (gypsum) which, where it was present, formed the white patches we had already observed from a great distance when approaching the island. The ground now became very hot, not however intolerably so, until about 30 feet from the apex a few rocks again offered a convenient seat, not affected by the heat of the ground. There the Aneroid barometer and the temperature of the air were observed in the shade of an umbrella.

About half way between these rocks and the highest point cracks and fissures commenced to intersect the ground, widening higher up to the breadth of several inches, where clouds of hot watery vapour issued from them. They were filled with sulphur, often accompanied with beautifully crystallised white needles of gypsum, and a sulphurous smell also accompanied the vapour (sulphurous acid). This smell was however not very strong and did not prevent us from penetrating the clouds, when we discovered that what had appeared from below as the summit was in fact the edge of a small crater, about 90 or 100 feet wide, and 50 or 60 deep. At that depth it had a solid floor of decomposed lava or tufa and volcanic sand. Its walls were made up of rocks, in appearance like those of the older lava and were highest on the north and south sides. Towards the west the crater opened with a similar cleft, to that which had permitted us

to enter the island. The vapours rose principally from the northern and southern quarters of the edge where the fissures were largest and longest, running both parallel and across the edge. The rocks where the sulphurous vapours issued from between them, were covered with reddish and white crusts, indicating the beginning of decomposition of their substance. From the top the horizon and more or less of the sea were visible in all directions, with the exception of the quarter between South and West. The inner slope of the circular elevation enclosing the valley, had no spurs, but was like a plain wall, falling off with a steep descent all round towards the centre. It had a uniform brownish colour, appertaining either to the surface of larger masses of the rock itself, or being derived from the dry grass and smaller shrubs covering the slope. There were no trees or brushwood visible to correspond to the richer vegetation on the external circumference. Horizontal parallel lines, traceable throughout the circle and rising somewhat like the borders of receding steps, indicated the thickness and strike of the different sheets of lava and tufa which, superimposed upon one another, formed the substance of the circular elevation. A very good transverse section of it had already attracted my attention, where the left side of the transverse valley debouches into the sea. Several strata of tufaceous formation, alternating with older rock like lava, could be seen there. rising from the rocky beach. 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. All these strata dipped outwards from the centre of the island, parallel with the external slope of the encircling wall. It is interesting to observe that this slope continues under the sea level on three sides of the Island at least, at the same inclination as above water, which averages about 35°. This is shown by the soundings, which exceed 150 fathoms at a distance of a quarter of a mile from the shore.

Judging from what we saw, as I have here attempted to describe it, I would conclude that the circular valley and its walls constitute the crater of a huge volcanic cone of sub-marine basis, which had