Solid Fragments Research Articles

Natural Glass from beneath Red Clay on the Floor of the Atlantic

DURING April and May 1961 on a cruise of the R.V. Chain, a programme of coring deep-sea sediments from the Atlantic for geochemical investigations was conducted. At 19° 23′ N., 40° 53′ W. a modified Kullenberg corer was lowered through 4,430 m. of water to the summit of a rise on the ocean floor. The topography of the sea bed in this region is irregular, but between the hills and rises the average depth is approximately 4,900 m. At the point where the corer struck the sea bed the surface sediment is a red clay, but no sediment core was obtained since at a very short distance below the surface the red clay is underlain by solid material. The corer struck and broke the surface of this solid material, a fragment of which was recovered in the pilot corer, together with the overlying red clay. From the position of the solid fragment in ther pilot corer the thickness of the clay can be estimated to be not more than 38 cm. The solid fragment is a very dark brown, almost black natural glass of irregular shape, but with approximate dimensions 3 cm. × 2.5 cm. × 1.3 cm. Two faces of the fragment were freshly broken surfaces. On two other faces a thin (1 mm.) zone of devitrification occurs with small areas of manganese deposition on the outer surface. The two other faces appear to be natural fractures. Internally the fragment contains small irregular cavities about which slight devitrification has also occurred. When collected the fragment showed a marked tendency to disintegrate into smaller fragments, a consequence, no doubt, of the impact of the corer on the brittle glass. Red clay containing broken shards of the same glass was found adhering to the piston of the main corer, and it is likely, therefore, that the glass formation is too extensive to be interpreted as a boulder contained within the red clay. It is believed to represent the solid surface on which the overlying sediments rest. So far as is known this is the first sample collected of solid rock indisputably from below the sediments of the deep Atlantic.

The Late Eruption of Vesuvius

OUR visit to the crater of Vesuvius on January 11, 1884, was a most interesting one. In my former letter I gave the rough details of this new eruption as well as could be ascertained from the base of the cone. The lava that issued on Tuesday night continued to flow till Wednesday evening, but seemed to have arrested its progress about 10 o'clock that night, when I was in the Atrio del Cavallo. This stream proved to have welled out at the base of the little cone of eruption and to have flowed across the solid lava plain in the crater of 1872, and then to have poured down the north-north-west slope of the cone till it reached the Atrio, across which it extended but little. Within the crater ot 1872 we have a somewhat convex plain of lava, which is continuous with, or, more properly, overlaps, the crater edges, except for a short distance on the south-south-west side. The northeast part of this is covered by the remnants of the crater of January, 1882. Within this were a series of crater rings that have since filled up to a certain extent the cavity of 1882. For some time the vent has travelled south, so that the present cone of eruption overlaps the crater ring of Januiry, 1882, on its south side, whereas there is a deep crescentic fossa between the present cone and the north crater ring of two years since. The vent was giving forth great volumes of vapour, and there was an almost continuous fountain of fragments of molten lava, which often attained the height of one or two hundred yards. As a consequence much filamentous lava, often as fine as cotton, was raining around the crater, and;as we sat there eating our lunch, it was so covered with these rock fragments, that it required a long climb on foot to make such a gritty meal palatable. The ejectamenta are composed solely of lava in detached pieces, ejected in a plastic state with a few bombs, consisting ot older solid lava fragments partially fused and rounded on the surface, which is varnished irregularly by the fluid magmi that enveloped them. This indicates that the lava is very near the top of the chimney, which must be full, as it has been for some time. Photography was no easy matter amidst this fiery bombardment, for such was the abundance of the ejectamenta that we could see how rapidly the cone of the eruption was growing. I made a rough calculation of the quantity of new material expelled, and 1 think six cartloads in four seconds as quite a fair estimate. The lava that had flowed was solid and cold enough to allow my dog to cross it with ease, though through a few cracks it was seen to be still incandescent, and a green staff thrust in immediately blazed. The lava that was flowing in the direction of Pompeii is still doing so in one or two points, apparently at the same rate and place as two weeks since.