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 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 the 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 out-wards 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 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
