The lava had first flowed towards the escarpment of Monte Somma in a fan-like manner, so that the eastern extremity reached that great natural section just beneath the Punta del Nasone Still following the natural inclination of the ground, it turned to the west, and on June 15 was opposite dyke 16 (as marked on my large geological map just published, and on the dykes themselves), advancing at a very slow rate.

The lava is a vitreous and coarse-grained rock, especially in regard to the included leucite as well as augite crystals, whilst the surface is, with one exceptional tongue, of the corded or 'pahoehoe' type. This is due to the magma being one that has been simmering since January in the chimney of the volcano, so that most of its dissolved water has been boiled off, and so allowing it to cool without the formation of scoriæ from the

FIG. 3.-Fumaroles formed on the new lava close to its exit at foot of great cone in the Atrio, as seen on June 15, 1891. (Photographed by the author.)

vapour that otherwise would escape after its exit. Leucite I have also demonstrated to be formed while the magma is simmering under low pressure with free escape for vapour in the upper part of the volcanic chimney.1

At the summit of the great cone the crumbling in of the edges was constantly going on, but the upper extremity of the lateral rift at the foot of the cone of eruption and at the summit of the great Vesuvian cone had nearly ceased to give forth vapour. Along the line of rent on the mountain side no fumaroles or other signs of activity were visible except quite at the foot, where those of which I have spoken commence.

Up till June 26 there was an effort to clear the upper part of the

See H. J. J. L., 'Geol. M. Somma and Vesuvius,' Quart. Journ. Geol. Soc. vol. xl. ; and Relationship of the Structure of Igneous Rocks to the Conditions of their Formation,' Scientific Proceedings Roy. Dublin Soc. vol. v. N.S.

volcanic chimney of the impeding materials, which were constantly being added to by the slips from the crater's edge; but on that evening a dull red glow was visible in the crater bottom, showing that a fairly clear passage had been temporarily made for the continuous escape of vapour, and also that the lava was at no very great depth from the summit of the volcano. This of course indicates that the lateral opening was insufficient to drain off much of the lava which occupies the chimney above the level of the lateral outlet. Had such evacuation really taken place the eruption would have assumed enormous proportions, from the actual amount of lava above the tap, but more from frothing up of lava below that level, in consequence of the relief of pressure which in that case would occur. Of course, during all these days the ejection of dust with the smoke occurred, giving the latter its peculiar dark grey colour. Further destruction of the crater edge took place, so as to partly block the outlet, and it was not till our next visit that it again cleared.

On June 30 I again visited the crater, accompanied by my friend Mr. A. Green. All the summit of the great cone was covered by a thick coating of dust and sand, upon the surface of which were the usual white and yellowish-green chloride crusts seen on such occasions, so rich in copper as to plate with that metal the iron nails of our boots. The crater had considerably enlarged, the edges were in an extremely unstable state, with often considerable strips marked off by cracks parallel to the free edge, so that with a slight push by a stick it was possible to detach large masses of the materials which form the sides of the crater in the recent cone of eruption. So dangerous were the edges that it was but two places that my experience indicated as being safe to approach and look over, and that even with several precautions; so that the fatal accident to Señor Silva Jardim, who lost his life here but a few hours after our departure, is not to be wondered at.

On looking down some 45 to 50 m. beneath us, we could see the glow from a mouth some 2 or 3 m. in diameter. The walls of the crater were concave, so that, although overhanging at the top, yet a plumb-line let fall from the edge would strike the bottom of the cliff. The crater bottom was roughly plain, due to the combination of a talus all round, and an attempt at a cone encircling the main vent. It will be thus seen that the crater cavity was of the form of a convex-sided cylinder, or more simply barrel-shaped, with its upper diameter some 50 to 55 m.

With much difficulty we made our way around to the north side of the cone of eruption, which did not show its usual loose scoriæ surface, as it was buried beneath a thick coat of sand and dust, covered with a thin saline crust on its surface. The upper limit of the radial rift, which we were prevented from examining three weeks previously, on account of its giving out so much vapour as to constitute the temporary escape aperture of the volcano, had now become quiescent, so that we could fully examine it. Only a current of hot air was now issuing from it, but I was able to collect some fine masses of crystallised molysite and kremersite from its edges. Its average breadth was about 0.50 m. where it traversed old compact lava, but of course it disappeared as soon as it reached the looser materials. The real azimuth of its orientation, which we could now determine with greater accuracy than when we were walking over hot rock and enveloped in hot irritating vapours, proves to be, as it radiates away from the axis of Vesuvius, about 15° west of north. It curves then a little to the north, and near the foot of the

great cone it again assumes nearly the same azimuth as at starting, an arrangement which is quite evident when the Vesuvian cone is regarded from the Punta del Nasone. From that, the highest point of Somma, the lower extremity of the rift lies a little to the right or west, and faces that part of the Somma ridge which corresponds to the upper extremity of the Vallone Cancherone.

In the forenoon of June 30 much dust had fallen at the lower railway

Limits of the crater of 1872; where overflowed by more recent lavas, a, and where
still uncovered, a'; remains of cone of 1885-86, b; part of crater edge of
May 1886, c; part of crater edge of May 1889, d; cone of eruption up to
June 7, 1891, ef; fissure of May 1889, g; yellow patches of decomposed lava,
scoriæ, and dust, h; fissures emitting hot vapour with HCl, i; guides'
shelter, j; numerous fissures at the S.E. edge of the crater plain and great
cone that the preceding days had increased in size and number, k; other
fissures on the N.E. of great cone, ; fissures along the edges of the crater in
process of formation, mn; present crater, n; dykes seen in section, o; hollow
dyke of the eruption of May, 1889-91, and of anterior ones, p; same of erup-
tion of May 2, 1885, q; vapour column hiding bottom of crater, r; fissure
of eruption of June 7, 1891, x.

station, of which we collected some bagfuls. It is the usual fine sandy material of these eruptions, and consists of the pulverised components of the cone of eruption.

Having passed the night at the lower railway station, the next day we crossed the Atrio, ascended to the western extremity of the ridge of Somma, and followed it along so as to get a general bird's-eye view of the whole scene of the eruption, and take photographs of the more important points. As one stands on the Punta del Nasene and embraces

that magnificent view of Vesuvius and the Atrio del Cavallo, one sees below the new lava-stream in the form of the letter, the horizontal portion of which is still being prolonged down the Atrio towards the Fossa della Vetrana. In the middle of the ridge we found a thin coating of fine red dust which had reached thus far from the crater. Much of the Atrio was also covered by the same material. Scaling the cliff face just beyond the Cognulo di Ottajano to the Atrio del Cavallo, we again visited the lower point of the outburst. Most of the beautiful fumaroles were in a state of ruin, and lined by good-sized crystals of hæmatite and mixed chloride crusts. Here the lava was quite solid, though at one point was a hole, some 50 m. from the base of the great cone, where we could see the molten rock flowing lazily along about a metre beneath our feet. The lava at the end of the flow was making considerable progress to the westwards, and stood opposite dyke 13.

During the month of July few changes took place in the mountain ; the crater still got larger, dust was thrown out, and the lava descended. These phenomena are capable of continuing for months if the drainage opening does not enlarge.

After an interval of a month, during which by the kindness of Messrs. Treiber and Ferber I was kept continuously informed of any change, I again visited the volcano. The crater had considerably enlarged, but chiefly in a south-easterly direction, in the line of the fissures that have existed for a long time at the edge of the crater plain and the top of the great cone. These fissures had also increased in size and number since my last visit, so that altogether this seems to be, at present, the most favoured direction for the next disruption of the great cone. The crater has therefore an irregular oval form, with the major axis directed N.W.-S.E. On this occasion I could not see the bottom of the crater, but on its walls were several dykes, which may be enumerated according to their orientation:-N.E.; N.; N.N.E., probably the dyke of the last eruption; N.W.; S.W., probably the upper part of the fissure i below which emits hydrochloric acid: the hollow dyke that has supplied the eastern rift; the hollow dyke that supplied the eruption of May 2, 1885; and a little solid dyke close to it. There may have been others, but the perilous nature of the crater edge requiring great care, even in the only two places one could approach, together with the abundant irritating vapour, prevented a careful examination.

The lava, which had at one time extended down to nearly opposite Messrs. Cook's gate-lodge in the Fossa Vetrana, was now flowing very slowly at the junction of the Fossa and the Atrio del Cavallo.

A few days previously four shocks of earthquake occurred, limited to the great cone and felt at the lower railway station. These, combined with the other phenomena above mentioned, show that the cone is in an extremely unstable state, and want of confidence must be felt until some time further has elapsed.

In conclusion, the reporter must thank Mr. G. M. Cook, of Messrs. Cook, Son & Co., for granting free passage over the Vesuvian Railway, thus greatly facilitating the investigation of the volcanic phenomena.

Second Report of the Committee, consisting of Professor JAMES GEIKIE (Chairman), Dr. TEMPEST ANDERSON, Dr. VALENTINE BALL, Mr. JAMES E. BEDFORD, Professor T. G. BONNEY, Professor W. BOYD DAWKINS, Mr. JAMES W. DAVIS, Mr. WILLIAM GRAY, Mr. ROBERT KIDSTON, Mr. ARTHUR S. REID, Mr. R. H. TIDDEMAN, Mr. W. W. WATTS, Mr. HORACE B. WOODWARD, and Mr. OSMUND W. JEFFS (Secretary), to arrange for the collection, preservation, and systematic registration of Photographs of Geological Interest in the United Kingdom. (Drawn up by the Secretary.) YOUR Committee beg to report that during the past year the work of collecting photographs illustrating the geological features of our country has been continued, with the result that 313 additional photographs have been received and registered, making a total up to the month of August of 588. A detailed list of these additional photographs is appended herewith. At the Leeds meeting of the Association upwards of 200 photographs were arranged for exhibition in the room appointed for the use of Section C, many of which illustrated sections of strata and other geological features of considerable scientific interest. This collection attracted much attention, and it is proposed to continue the exhibition at Cardiff if convenient arrangements can be made. By this means the Committee hope to secure the aid of many photographers, who can thus form a better idea of the kind of subjects which it is desirable to include in the collection of geological views.

Special efforts have been made to induce the local societies in each county to organise systematic surveys for the furtherance of the work. This method has been pursued with great success in Yorkshire, the members of the Geological Photographic Committee of the Yorkshire Naturalists' Union having again contributed a large and valuable series of prints. Many of these subjects refer to sections which cannot be reproduced, as, for instance, fossil trees laid bare in quarrying and excavations for the foundations of buildings now covered over.

The Hertfordshire Natural History Society and the East Kent Natural History Society have also organised schemes for the photography of local geological features, and some views have been sent in from these sources, which, it is hoped, will be supplemented by a further series next year.

In the case of some local societies difficulties have arisen, which have delayed the completion of similar arrangements proposed to have been made. It is not always possible to obtain the services of a photographer when desired, and it has been found difficult to arouse the interest of many of the local photographic societies in geological work. Considering the number of amateur photographers now to be met with in every centre of scientific energy, it is hoped that a large number of photographers will be induced in the future to co-operate with the local scientific societies in the scheme instituted by the Committee. The numerous field-meetings and scientific excursions, now so popular a part of the work of such societies, would appear to afford convenient opportunities for aiding our scheme, if arrangements could be made for a photographer to accompany the party whenever the district to be visited offered suitable subjects for the

1891.

Y