2. "Contributions to the history of the Deer of the European Miocene and Pliocene Strata." By Prof. W. Boyd Dawkins, M.A., F.R.S., F.G.S.

3. On the occurrence of Branchipus (or Chirocephalus) in a fossil state, associated with Archæoniscus, and with numerous Insectremains in the Eocene Freshwater Limestone of Gurnet Bay, Isle of Wight." By Henry Woodward, Esq., F.R.S., F.G.S.

4. "The Chronological Value of the Pleistocene Deposits of Devon." By W. A. E. Ussher, Esq., F.G.S., of H.M. Geological Survey.

In this paper the author endeavoured to work out the sequence of events indicated by the Pleistocene deposits of Devonshire. He believed that during late Tertiary times subsidence extended to the south-western counties; and to this he ascribed with some doubt the accumulation of a patch of gravel on the north summit of the Black Downs and of part of the old bone-breccia of Kent's Cavern. In the Glacial period, with the increase of cold, snow accumulated on the high lands, with formation of glaciers, which descended and united to form a great ice-field, planing the surface of a district composed chiefly of Cretaceous and probably Tertiary strata. To this period the author ascribed the formation of the clay with unworn fragments of flint and chert, and, doubtfully, part of the clays of the Bovey valley, the clay of Petrockstow, and part of the bone-breccia and the crystalline stalagmite of Kent's Cavern. The Postglacial phenomena he referred to three subperiods, in the first of which, during a gradual amelioration of the climate and disappearance of the ice, large quantities of surface-water were set free, redistributing and removing Tertiary outliers, partially destroying the old ice-beds and moraine rubbish, and sweeping Secondary deposits from Palæozoic districts. The deposits then formed were supposed to be the old gravel patches of Colford and Orleigh Court, the waterworn materials on the Blackdowns and Haldon, the sands flanking the Bovey valley, and, with doubt, the redistributed Triassic pebble-beds of Straightway Hill, and part of the cave-earth of Kent's Cavern. The next subperiod he regarded as one of great fluviatile action, the land being higher than at present, though sinking, and the meteorological conditions such as to greatly increase the volume of the rivers. The subsidence having continued to the level of the present raised beaches, reelevation took place, producing greater cold and more extreme seasons, and culminating in the production of continental conditions, permitting the southward migration of a temperate fauna, and the advent of one requiring greater cold. During this period the gravels connected with the formation of the present valley-system, the raised beaches, and the "Head" were produced, and, doubtfully, part of the cave-earth and the granular stalagmite of Kent's Cavern, and the clay of Petrockstow and Roundswell. In the last subperiod the author considered that a subsidence took place, during which most of the valleys were

excavated to their present depth, and forest-growth took place upon the old marine plain. The forests were then gradually circumscribed by the encroaching sea and diminishing rainfall, which also led to changes in the streams; and finally the sea entombed the forests and swamps on the coasts, and produced the present cliff-line. The results of this period are the submarine forests, most of the rivervalley gravels, and alluvial tracts bordering the present river

courses.

January 9, 1878.-Prof. P. Martin Duncan, M.B., F.R.S.,

President, in the Chair.

The following communications were read:

1. "On the Great Flat Lode south of Redruth and Camborne." By Dr. C. Le Neve Foster, B.A., F.G.S.

The author described the mode of occurrence of the stanniferous deposit known as the Great Flat Lode, the mines worked in which extend for a distance of 3 miles, and furnish about one eighth of all the tin raised in Cornwall. The mines in question are Wheal Uny, South Carn Brea, West Wheal Basset, South and West Wheal Frances, South Condurrow, and Wheal Grenville; and in all the lode dips at a much less angle than the average of Cornish veins, the dip at Wheal Uny being only about 46° S. Throughout the lode contains a small leader, usually only a few inches wide, occupying the space due to the shifting of the two sides of a fissure, and filled partly mechanically, partly chemically. Above, or below, or on both sides of this there is a mass of stanniferous schorl rock from 4 to 15 feet wide; this contains from 1 to 3 per cent. of cassiterite, in little grains, or in strings or veins. Schorl rock, very poor in tin (locally called capel or greyback), separates the lode from the surrounding granite or killas, but passes on one side into the lode, and on the other into the granite or killas, so that no wall is recognizable. From these characters the author inferred that the lode and the capel are merely altered rocks, the fissure now occupied by the leader having served to bring up vapours or solutions which have entirely changed the rocks on both sides of it. In support of his opinion, the author adduced other instances of the change of both granite and killas into schorl rock; and further stated that, both at South Condurrow and Wheal Grenville, he has found in the schorl rock cavities as large as a pea, agreeing in form with crystals of orthoclase felspar.

2. "On some Tin-mines in the Parish of Wendron, Cornwall.” By Dr. C. Le Neve Foster, B.A., F.G.S.

The mines described in this paper are called Balmynheer, The Lovell, and South Wendron. In the former the stanniferous deposit consists of a large irregular mass of rock 30-50 feet thick; its dip is N., at an angle of about 30°, and its strike E. 32° N., along which it has been traced for 36 fathoms. The tinny rock is separated from the granite above by a slide or vein of white clay, with

a little quartz and mica, about 6 inches thick, but passes insensibly into the granite below. At the Lovell Mine there are two lodes, north and south, the former striking from 37° to 45° N. of E. and dipping N.W. at an angle of about 70°, the latter running E. 48° N. and dipping N.N.W. about 60°, so that the two lodes unite in going eastward and in depth. The lode is separated on one or both sides from the adjoining granite by a rock locally known as "cab," 6-12 inches thick, composed of quartz, mica, gilbertite, chlorite, iron-pyrites, copper-pyrites, and a little schorl. The lode itself shows joints which are mere planes of division in the rock, and usually have the same strike and dip. Divergent joints also occur; and where these traverse the granite they carry with them a little tin-stuff for some distance. The South-Wendron Mine is worked in an irregularly cylindroid pipe of tinny rock, merging gradually on all sides into the granite; the shorter axis of its oval section is about 10 feet, while the longer axis varies from 20 to 60 feet. It dips at an angle of 49° in a direction N. 25° W. The stanniferous rock in these mines is essentially a mixture of quartz, chlorite, gilbertite, iron-pyrites, and tinore, with zinc-blende in some cases, and usually some mica; fine needles of tourmaline occur in the cavities which it encloses. In the South-Wendron Mine the southern part of the pipe is sometimes very granite-like in appearance, consisting of pink orthoclase crystals imbedded in a mass of quartz, chlorite, mica, and iron-pyrites, with a little copper-pyrites, fluor, and tin-ore. One specimen is a true stanniferous granite. These characters lead the author to the same conclusion he has arrived at in the case of the Great Flat Lode, namely that these tin deposits consist entirely of altered granite, and are not ordinary mineral veins: they have no walls, but the stanniferous rock passes gradually into granite; and they show no signs of banded structure due to the successive deposition of minerals. The highly granitic character of part of the South-Wendron tin deposit is strongly confirmatory of this view, which is further supported by the occurrence, in the dark mass of the so-called lode at the Lovell, of pseudomorphs of quartz after orthoclase containing a little cassiterite.

3. "On some of the Stockworks of Cornwall." By Dr. C. Le Neve Foster, B.A., F.G.S.

The author commenced by explaining that the term "Stockwork” had been derived from the German Stockwerck, meaning "Storywork," in allusion to the method of working in steps or stories in open workings, originally adopted for such deposits. Their being worked in open quarries affords a good opportunity of studying the mode of occurrence of tin; and many of them are interesting on account of the small percentage of tin which will cover all expenses. Thus, in the Wheal-Prosper Mine, the average amount of oxide of tin obtained per ton of stuff is not more than 3 lb., worth, at the present price of "black tin,” 44d. per lb.; so that the ground as it stands is only worth 13d. per ton. The mine can be worked without loss, on account of the softness of the rock and the large size

of the grains of tin-ore, the comparative lightness of the substances associated with it, and the command of water-power.

The deposits worked as stockworks occur in Cornwall in killas, granite, and elvans. The tin-ore, associated with quartz and with small quantities of other minerals, is found in more or less parallel thin veins and strings, dipping at a high angle, and occasionally giving off branches or uniting with one another both in dip and strike. In the killas the rock close to the veins is occasionally altered into tourmaline-schist; in the granite the walls of the veins, and sometimes the whole mass of granite, are altered into greisen and schorl rock. At Carclaze the orthoclase of the intervening bands of granite has been converted into china-clay, which is now the main object of the working. At Carrigan the leader sometimes adheres to the enclosing rock by one side only, the other being bounded by a clay vein which contains broken crystals of cassiterite, indicating, in the author's opinion, that a movement of the walls has taken place since the deposition of the tin-ore. Of the stockworks in elvans the author gave a list, and remarked that the elvan of the Terras Mine is particularly interesting, as it presents a series of cavities left by the removal of orthoclase, and now being filled up with schorl and a little oxide of tin.

4. "The Precarboniferous Rocks of Charnwood Forest.-Part II." By the Rev. E. Hill, F.G.S., Fellow and Tutor, and the Rev. T. G. Bonney, F.G.S., Fellow and late Tutor of St. John's College, Cambridge.

The authors described the result of the microscopic examination of a considerable series of the clastic rocks of Charnwood. Many of these, even among the finer beds, prove to be of pyroclastic origin. The coarser are generally composed of a groundmass of pulverized felspar, with viridite and some iron peroxide, full of larger fragments of felspar crystals (generally both of orthoclase and plagioclase) and lapilli. The structure of these is often distinct, some are certainly andesites, others some kind of trachyte; slaty fragments are also present, and occasional grains of quartz. The authors express their opinion that all the larger felspar crystals, and most, if not all, the quartz grains, are of clastic origin, even in the more highly altered varieties. Some of the larger fragments in the breccias were examined, and referred in part to devitrified trachytes not very rich in silica. The igneous rocks were then described. The syenites of the southern and northern districts were shown probably to belong to one system of intrusion. The hornblendic granite of the Quornden district was also described, and the microscopic structure of the different varieties of it and the above investigated. A number of igneous rocks generally forming dykes in these was described: some appear to be altered basalts, others andesites; one is a felsite, another a diorite. A group of outlying igneous rocks in the vicinity of Narborough was described. Of these, one is a quartz felsite with some hornblende; another varies between this and a

quartziferous syenite; the rest are syenites; and one contains so much plagioclase as to be almost a diorite. One of the above, near Enderby, is seen to be distinctly intrusive in an altered slaty rock, which the authors have no doubt belongs to the Forest series. This discovery proves the igneous character of these rocks also, and extends the area of the slaty series 5 miles further south than was previously known. A section was devoted to the faults of the Forest region. Here the principal fault runs along the anticlinal axis, with a downthrow on its eastern side which diminishes from 2500 feet at the north end to 500 feet at the south end. East of this the beds seem undisturbed; but on the west they are shattered by many faults, whose course cannot be traced. These are most numerous near Whitwick. The anticlinal fault is Precarboniferous.

In conclusion, the age of the clastic and of the igneous rocks was discussed. The authors inclined to the opinion that the former are of the same age as the Borrowdale series of the Lake district (Lower Silurian), but admitted that the recent discovery of agglomerates in the Precambrian rocks of Wales, and in the probably Precambrian ridges of the Wrekin district, weakens the arguments for this correlation. They do not think that there is any reason for supposing them Cambrian. If the Charnwood series is Lower Silurian, they think it most probable that the syenites and the Quornden granite were intruded in some part of the Old-RedSandstone period, and that the later dykes were very probably Postcarboniferous but Pretriassic.

XXXV. Intelligence and Miscellaneous Articles.

ON SOME MEASUREMENTS OF THE POLARIZATION OF THE LIGHT COMING FROM THE MOON AND FROM THE PLANET VENUS. BY THE EARL OF ROSSE, F.R.S.

*

SEVERAL years ago, at the suggestion of a friend, having examined some portions of the lunar surface with a Nicol's prism with a view to the detection of small sheets of standing water, if any such chanced to exist, I was led on to make a rather extended examination of particular portions of the surface with the polarimeter, under the idea that if the precise position of elongation from the sun where the polarization of a point of the lunar surface attains a maximum could be accurately determined, it might be possible to obtain an approximate value of the refractive index of the material composing that surface, and so to distinguish between material of a vitreous nature, ejected from volcanoes, and a surface of ice and

snow.

The subject has been invested with the greater interest from the fact that Arago, having found the maximum of polarization of the whole of the moon's light to occur at or near quadrature, From the Proceedings of the Royal Dublin Society, May 21, 1877. Communicated by the Author.