APPENDIX.

Report on the Chapelhall Clay. By Mr. DAVID ROBERTSON, F.G.S.

Millport, May 5, 1894.

The samples of clay that were submitted to me for examination from Chapelhall from depths of 14 to 17 feet were, as taken from the pit, of a dark slatish colour, and when dry of a light grey colour. The mud referred to in the following list is that portion of the clay that passed through a sieve of 96 meshes to the inch, and the sand is what passed through a sieve of 24 meshes to the inch, and the stones are those retained in the same sieve. That which is commonly called 'floats' is that which rises to the surface of the water when the clay is dissolved, after having been dried. The dissolved clay, when stirred up, retained its dark colour, but after standing a little a reddish brown formed on the surface.

The floats' are not referred to in the subjoined list, as they were all alike in being quite barren of animal remains, and almost of everything else.

From the Well.-No. 1. Depth, 14 ft. to 14 ft. 6 in.

The sand consists of white and black grains, the white preponderating greatly, or, I may say, with a small mixture of black grains, both apparently rough or angular.

The stones mostly water worn, a few portions angular. Few striations were noticed. This may be accounted for as few of the stones are such as would readily take and retain the markings.

The sand consists of white and black grains, mostly white, both angular. The stones more or less water worn, but not to any great extent. Many pieces were angular, some appear to have been crushed. No striations were noticed.

The sand consists of white and black grains, chiefly white.

Stones mostly water worn. The pieces of shale generally more or less striated, or indented, or both, and a few bits of coal, some with marks

of abrasion. Also bits of vitrified stone. These show no marks of rubbing or of having been much rolled about. In this sample a small fragment of a valve of a bivalve shell imbedded in a piece of Carboniferous shale.

The sand consists of white and black grains, the white prevailing greatly.

Stones mostly water worn, the lesser portion more or less angular. Most of the bits of shale are striated or indented. The coal here has

The sand light grey.

Stones mostly water worn. Many pieces of coal and small pieces of

slag.

From the Bores.-Bore No. 1. Depth, 14 ft. to 17 ft.

Stones mostly water worn. Many small pieces of coal, some abraded, and three small bits of slag.

Stones mostly water worn, only one piece noticed striated. A few pieces of coal, some with marks of rubbing. Some bits of slag.

In this bore the stones are all small, and from the absence of larger and heavier ones the proportion of mud is more and that of the stones less. No striation was noticed. Coal and small bits of slag were present.

As stated above, the floats were not taken into account, as they were all alike in being quite barren of animal remains and almost of everything else, which is a very different condition of things from the abundance of float

that we generally find in the post-Tertiary shell-bearing clays. The samples of sand are of a very uniform colour, and any little variation that appears may have been caused by the black grains being lighter and coming more to the surface than the white in one case than another.

From the abrasions on the above samples of coal, there can be little doubt that it belonged to the deposit.

As no rubbing is noticed on any of the pieces of slag, and the fractured edges appearing sharp, it is most likely that it got into the clay accidentally. At the same time it is curious that it is met with in so many of the samples both of the pits and bores.

So far as I can judge from the samples of the clay and the average proportion of stones and mud, also the paucity of the floatings, and the entire absence of animal remains (with the exception of a small fragment of shell embedded in a piece of Carboniferous shale), I have no doubt whatever that the deposit is characteristic boulder-clay.

The Volcanic Phenomena of Vesuvius and its Neighbourhood.-Report of the Committee, consisting of Mr. H. BAUERMAN, Mr. F. W. RUDLER, Mr. J. J. H. TEALL, and Professor H. J. JOHNSTONLAVIS. (Drawn up by Professor H. J. JOHNSTON-LAVIS.)

Vesuvius. Since the last report lava has continued to pour forth from the top of the new lava-cone in the Atrio del Cavallo, sometimes in small quantities, at others in considerable abundance. On no occasion, however, did the lava issue beyond the limits that it had reached in the years 1891-92. In fact, the whole of that eastern part of the Atrio known as the Val d'Inferno has not been invaded at all by the new lava during or since its issue in the spring of 1891. The consequence of this has been that it has continued to pile itself up around the line of fissure by which it issued, and still further add to the dimensions of the great lava-cone that it had built up in the Atrio. So great has this cone become that it constitutes a prominent feature in the outline of the volcano as seen from Naples. The eminence of Somma is separated from Vesuvius by the depression of the Atrio. This notch, so to speak, in the general outline was terminated below by an almost horizontal line, which is now replaced by an obtuse cone, so that many people speak of three summits to the Vesuvian volcano. This is rather an exaggeration, for although the new lava-cone is of very considerable dimensions, for the time occupied in its growth, yet it cannot compare with that of the cone of Vesuvius on one side or the ridge of Somma on the other.

The whole of this new cone is entirely built up of lava, by far the greater part being of the pahoehoe or corded type; only now and then during marked activity has there been produced any lava with a rugged scoriaceous surface. The occasion was therefore a very valuable one to determine the slope of such a lava-cone. This was done only normally to the line of fissure by which the lava issued, and which makes the cone terminate in an elongated ridge rather than in a point. Practically all these clinometric observations, which were taken with great care, gave angles varying from 13° to 15°.

Comparing this angle with that of such mountains as Etna or Mauna Loa, we must consider that both are composite cones, have experienced many disturbing influences such as the formation of parasitic erup

tive outlets from which lava streams have issued far away from the summit, and have thus diminished the general slope of the volcano. Those mountains are usually considered to have an average slope of 10°. The Hawaiian lavas are, as is well known, exceptionally fluid, and we could hardly expect cones of greater slope than 10°. At Etna the lavas have always been more viscous from their lower temperature and the compound or false viscosity given to them by the large number of porphyritic crystals already existing in the magma at the time of emission, just as earth mixed with water may produce a viscous mud. These new lavas of Vesuvius, as is the case with all those that issue high up on the volcano and in small quantities, were very viscous owing to their low temperature and advanced crystallisation, so that soon after the material poured out it was prevented from flowing by slight further cooling. We may take therefore this average slope of 14° as the best and most correct estimate for a lava of this nature.

This recent outflow exhibits most of the varieties of surface to be met with in the type of lava above mentioned, such as corded shapes of different kinds, irregular globular surfaces, sheets, and plates either in position or reared on end, and tunnels of every variety, frequently with continuations as walled canals, of which a good example is seen in the photograph exhibited. A magnificent lava hump is to be seen in another photograph, and was formed right under the escarpment of Somma. The origin of these humps is still obscure. They are common on most large flows of corded lava of Vesuvius, but unfortunately I have never been present at their formation, nor do I know of anyone who has.

The points of issue of the lava occurred at various spots along a line corresponding with the strike of the radial dyke to which it owes its origin, so that the new lava has as a summit an irregular ridge running nearly north and south. Of course the actual highest point is nearly always that where the last lava issued. Generally more than one spot along this line gave out lava at the same time. The fluid rock flowed sometimes on one side, sometimes on the other, so that the general public at Naples were only from time to time treated to a glimpse of Nature's fireworks, and when the lava flowed in the opposite direction it was often announced that it had altogether stopped.

During the last year several new conical spiracles were formed, but none of them comparable in perfection of form to those described in the last two reports, or exhibiting equally interesting features.

No very interesting minerals were produced as sublimates. In fact, only two species are worthy of mention. On one occasion a small quantity of tenorite was formed in one of the spiracles. Soon after the lava had entirely stopped flowing in February, sublimates of potash-bearing halite were very abundant around about the vents, in beautiful fern-like skeletons, in which a number of feathery branches radiated at right angles from a stem representing usually about three edges of a cube, and were themselves so many edges of smaller cubes. Sometimes this halite was grey, from minute hæmatite crystals being deposited with the salt, which likewise was in some cases greenish from copper impurities. Most, however, was of a beautiful snow white. One small cave in particular, about the size of a man's body, was clothed with the most glistening white lining, and from the roof and walls showers of crystals fell from time to time. These were not visibly red-hot in bright diffused daylight, but looking towards the shaded inner extremity of the cavity a bright red incandescence was visible.

In a short time, with suitable apparatus, I collected over two kilogrammes of this material absolutely free from mechanical impurities.

Along many of the cracks of the lava beautiful glassy crusts of halite, more or less impure, were formed, and often showed a dull red heat in daylight. These crusts on being removed become rapidly opaque and milky in hue, and audibly cracked into starch-like columns, due to the rapid contraction on cooling-producing, in fact, a miniature basaltic structure.

About February 5, 1894, the lava was issuing in very small quantity, and by the 7th showed no trace of movement. Yet even in May cracks in the lava near its point of exit were incandescent some distance in, and the saline incrustations mentioned above were in full perfection.

Coincident with the arrest of the lateral outflow, the lava rose in the chimney and the red reflection from the top of Vesuvius that had been absent for so long, with rare exceptions, was again almost daily visible. The level of the lava in the main chimney soon rose to the bottom of the new crater that had been forming, and increasing in size during the time the lateral issue of lava had been going on, and commenced the filling up of that cavity by the formation of a cone of eruption, so that almost coincident with the arrest of the leakage of lava laterally the central activity changed from the crater- and dust-forming stage to the lava cake- and cone-forming stage.

I made a careful examination of the summit of Vesuvius about the middle of May. The crater in an east and west direction was about 150 m. in diameter, and its depth, then decreasing, was about the same. The walls were remarkably steep, in some places even vertical or overhanging. The bottom could be seen with difficulty owing to the crumbling nature of the edges. The walls are nearly all covered by sublimates or dust that has adhered and crusted them over, so that several dykes both solid and hollow can no longer be distinguished. This is especially the case with the one formed during the 1891 outburst. The details of the great rift of the 1880-81 and subsequent eruptions on the east side of the great cone were still easily discernible. On the south side, and a little to the east, a wall of rock stands out from the side of the crater and is directed nearly towards the centre. It is capped by a pinnacle of rock, and is really the old dyke of the 1885 eruption.

Just to the east of that wall, and partly owing to its existence, the slope of the inside of the crater is less in that direction. Here the guides had made a little path for a few metres down. On examining carefully the condition of things from its lower termination, which so far aided little the view of what was going on at the crater-bottom, I found that by extending it down a slope, and then cutting a ledge farther round to the east at a suitable point, a bracket-like platform some metres square could be reached, which is about half-way down the crater. Later the path was further widened by me and made more commodious, and now gives easy access to the platform from which one can look right into the vent of the volcano and watch with ease the boiling up of the lava and the ejection of the great blobs and cakes that are rapidly filling up the crater. Unfortunately, owing to the well-like shape of the crater, the shadows due to the vapour column spreading out overhead, and the dark colour of the rocks, instantaneous photography could not be utilised to record this interesting and ever-changing scene.

As is usual at some period after an eruption, feathery gypsum is a common product in the cavities of the old scoriæ, and is associated at the