Page images
[ocr errors]

region is north-west and south-east, or north-north-west and southsouth-east. The country is traversed by several large doleritedykes.

II. The Northern Part of the East Coast.—Dolerite-flows predominate along the coast, and from their character are believed to have flowed from such fissures as are indicated by the doleritedykes noted in the preceding section. Some felsites, probably lavas, and felsitic breccias were also observed; also a granitite penetrated by epidiorites, and associated with chiastolite-slates. Many other rocks, schists and eruptives, were found.

III. The Northern End.—Sedimentary rocks (sandstones and limestones) are extensively developed in this section, as well as much volcanic material. The sediments are of Jurassic and Cretaceous ages. The volcano Ambohitra is situated on these sediments, and has poured out olivine-basalts. Shells of recent species occur on the mountain-chain at the northern end.

IV. The North-western Coast and Islands.--Marine strata of Jurassic, Cretaceous, and Eocene ages are found in this area, together with various igneous rocks including trachyte, foyaite, nephelinephonolite, hauyne-nepheline-phonolite, andesite, and basalt. "Southwest of Anorontsanga are four islands—three composed of volcanic rocks, and the fourth, Antanifaly, of nummulitic limestone.

3. “On a Collection of Fossils from Madagascar obtained by the Rev. R. Baron. By R. Bullen Newton, Esq., F.G.S.

The fossils forming the subject of this paper were collected in the northern part of the island. The author gives an account of the previous work on the fossils of Madagascar; this is followed by a description of the post-Tertiary, Tertiary, Cretaceous, and Jurassic fossils. The post-Tertiary fossils are for the most part terrestrial shells found on Ambohimarina hill, mainly of species still existing on the island. A few marine forms have been found elsewhere.

A description of species, many of them new, follows; and the author furnishes a list of all recognized fossils from the island, concluding with notes on certain limestones, including a Globigerinalimestone and one containing Girvanella. December 5th.—Dr. Henry Woodward, F.R.S., President,

in the Chair. The following communications were read :

1. Supplementary Note on the Narborough district (Leicestershire).' By T. G. Bonney, D.Sc., LL.D., F.R.S., F.G.S., Professor of Geology and Mineralogy in University College, London.

The author revisited this district, briefly described by himself and Mr. Hill in 1878, at Easter 1893 and in September 1894. The old excavations had been greatly enlarged, but little of importance had been disclosed : no dykes and no new junctions with sedimentary rocks. But the crystalline rocks have been recently struck in a fresh locality between Narborough and Huncote, about half a mile west of the pit near the former village. As in that case,

[ocr errors]

the rock lay very near to the surface; here the highest part of the boss was barely covered. The rock is hardly to be distinguished from that of the Narborough pit. The enlargement of the pit south of Enderby has exposed fresh sections of the junction of the slate and syenite, which has been now traced along the whole length of the pit from north to south, and some particulars are added to the former description.

The enlargement of certain of the pits has displayed some interesting sections of Boulder Clay resting upon the crystalline rocks. The latter are not appreciably ice-worn. The fragments in the Boulder Clay, identified by the author, were from the Carboniferous, Trias, Jurassic (especially Lias), and Upper Cretaceous formations. They indicated, in the main, a drift from more or less north-easterly direction.

2. “The Tarns of Lakeland.' By J. E. Marr, Esq., M.A., F.R.S., Sec.G.S.

The author has examined several tarns of the English Lake District. In those cases where the stream issues from the tarn over solid rock, ḥe finds either (1) direct evidence that the tarn results from the blocking up of part of a pre-existing valley by drift, causing the deflexion of the water to a direction different from that of the original stream in this locality; or (2) evidence which is perfectly consistent with such an explanation of the origin of the tarn.

Under the circumstances he would submit that tarns cannot be assumed to lie in rock-basins simply because the issuing stream flows over solid rock (and this assumption has been made), but that those who maintain the existence of such rock-basins must prove the occurrence of solid rock entirely around the tarn.

3. • Description of a New Instrument for Surveying by the Aid of Photography, with some Observations upon the Applicability of the Instrument to Geological Purposes.' By J. Bridges Lee, Esq., M.A., F.G.S.

The instrument described in this paper consists essentially of a photographic camera fitted inside with a magnetic needle, which carries a vertical transparent scale divided and numbered to 360°, and also with cross fibres which intersect at rigl.t angles. The fittings and adjustments of the instrument are of such a character that the camera can be accurately levelled and directed towards any point in a horizontal direction, and when a photograph is taken in an ordinary way the bearing of the median vertical plane which bisects the instrument through the photographic lens will be recorded automatically on the face of the photograph.

The vertical fibre (and its image on the photograph) serves as an index to read the bearing; and the same fibre marks by its shadow a line right across the photograph, which marks the median vertical plane on the image. The horizontal fibre is adjusted to mark on the image the horizontal plane which bisects the photographic lens.

[ocr errors]

The camcra re-ts on a divided horizontal circle, which can be adjusted to a truly horizontal position by levelling-screws. There is a tripod stand and head, with suitable appliances for supporting and adjusting the instrument in position. The camera is provided with a rectilinear doublet lens and iris diaphragm and rack-andpinion focussing adjustment. It is made of aluminium, and it is surmounted by a telescope adjustable in altitude and fitted with vertical and horizontal webs; and it is also surmounted by a revolvable tubular level.

The details of construction and the peculiar features and adjustments of the instrument are fully described in the paper, and some of the chief purposes to which it may be applied in furtherance of geological research are pointed out. The maker of the instrument is J. J. Hicks, of 8 Hatton Garden.

[ocr errors]


4. The Marble Beds of Natal.' By David Draper, Esq., F.G.S.

A crystalline limestone of enormous thickness' was mentioned by Mr. C. L. Griesbach, in 1871 (Q. J. G. S. vol. xxvii. p. 56), as occurring along the lower course of the Umzimkulu, in the county of Alfred, in the southern part of Natal. Since the time of his visit there the country has been opened out by settlers, and some attempts have been made to utilize this marble. The chief mass of this rock is met with at about 7 miles iuland, in the Indwendwa hill-range, within the fork formed by the junction of the Umzimkulu and the Umzimkulana, over 700 feet above sealevel, and continuous with the tableland westward. This consists of granite, overlain by the massive marble, roughly stratified, which is denuded north and south of the hill into the gorges of the two rivers, and is continued on the opposite flanks until cut off by faults. The north fault divides it from the Table-mountain Sandstone lying on clay-slate; and the south fault divides the granite from the Table-mountain Sandstone and clay-slate. The bedding of the marble dips towards the rivers, on each of their flanks, and strikes E. and W.

In quality the marble varies from coarse to fine-grained, and in colour from pure white to deep red. The coarse-grained variety contains 5 to 13 per cent. of carbonate of magnesia. Calcareous tufa, in some places several feet thick, has been formed from the marble.

From the junction of the two rivers eastward, slate is seen below Table-mountain Sandstone; and on the latter is a long stretch of the Dwyka Conglomerate to the coast, greatly disturbed for the most part, and pierced by two dolerite-dykes, between which a patch of Ecca Shales is preserved.

The author concludes that the marble was deposited on the granite, and probably on the Malmesbury Slates near by, before they were disturbed; that it does not extend far under the neighbouring hills ; and that some of its local detritus indicates that the riv ers ran at higher levels within relatively recent times.

December 19th.—Dr. Henry Woodward, F.R.S., President,

in the Chair. The following communications were read :

1. “The Lower Greensand above the Atherfield Clay of East Surrey.' By Thomas Leighton, Esq., F.G.S.

This paper embodies the results of the author's examination of the Lower Greensand of East Surrey during the three years 1892-94; and it is stated that two papers published by the Geologists' Association (vol. xii. pp. 4 & 163) are to be taken as introductory to this one.

The area discussed in this paper extends from Leith Hill in the west to Tilburstow Hill in the cast; and the divisions of the Lower Greensand chiefly referred to are those hitherto kuown as tbe Bargate, Sandgate, and Hythe Beds. The author states that the Lower Greensand of East Surrey shows that formation to consist of beds deposited in a marine estuary or narrow sea, not far from land and within the influence of strong currents, extending generally from N.W. to S.E., so that, without palæontological evidence, no correlation of beds here with those exposed at Sandgate and at Hythe is possible. He arrives at this conclusion by following the outcrop of the various chert-beds, which, after Dr. G. J. Hinde (Phil. Trans. Roy. Soc. vol. clxxvi. 1885), are accepted as of sponge origin (deep-water deposits), and further by following the outcrop of the pebble-beds, described by Mr. C. J. A. Meyer (Geol. Mag. for 1866, p. 15).

In Part 1 of the paper the author discusses the district to the west of the Mole, and endeavours to show that the view set forth in the Weald Memoir of the Geological Survey, to the effect that between Dorking and Leith Hill the lower horizons of the Lower Greensand undergo a change in composition, although possibly verbally correct, is geologically incorrect, since the lithological change is from south to north, from beds laid down in deep water to beds laid down in shallow water. In his communication to the Geologists' Association of last year, tho author showed that the pebble-bed at the base of the Folkestone Sands was at Abinger intimately associated with the Bargate Beds; and he now states that he has identified this pebble-bed in the Dorking-Horsham road section, described by Prof. G. S. Boulger and himself in 1892, and at two other places to the east. The drifts of the same neighbourhood are then discussed, and it is found that at the top of and on both sides of the Lower Greensand escarpment, which, as stated by the Geological Survey, is here saudy throughout, there are gravels obviously deposited by a considerable stream consisting chiefly of Lower Greensand chert (entirely of Lower Greensand material) with, amongst the rougher material, lenticular beds of fine pebbles composed chiefly of débris from the Bargate Beds. Fragments of Lower Greenrand chert have been obtained from the alluvium or from the beds of the streams now draining the Weald area to the south of Dorking. The soil over the Weald Clay as far south as Holmwood Common has everywhere yielded to the author fragments of the same chert. Hence it is argued that the chert-beds now seen upon Leith Hill to

[ocr errors]

the west formerly existed over the Weald to the south of Dorking, and that the fragments now lying about the surface have been left by denudation, as described by Dr. G. J. Hinde (op. cit.). Since, however, as has been stated, the present Lower Greensand escarpment to the north consists of sandy beds’ only, there must be a lithological change from south to north (deep-water beds to shallow).

Part 2 of the paper is devoted to the district east of the Mole. Where the escarpment rises above the alluvium of the river, the author finds the Bargate Beds with pebbles (at Park Hill, Reigate) separated from the Folkestone Sands only by a thin bed of Fuller's Earth and a layer of sandy chert. The section is now first described ; the dip has been observed and proved, and by measurement this pebble-bed is shown to lie at approximately the same horizon above the Atherfield Clay as when it was last seen west of the Mole. From Reigate eastwards to Tilburstow Hill the same beds are seen in the numerous hollow lanes and pit-sections. The pebble-beds are found approximately on a definite horizon; but whilst they become of less importance eastward, the overlying cherts, first seen at Reigate, become of greater importance in that direction. The thin bed of Fuller's Earth, also first seen at Reigate, thickens to the east likewise,

2. • On the Eastern Limits of the Yorkshire and Derbyshire or Midland Coalfield. By W. S. Gresley, Esq., F.G.S.

The author attempts to throw light on the question of the easterly extension of the Yorkshire, Derbyshire, and Nottinghamshire coalfield beneath the newer rocks. He notices the general trend of the strata, the sizes of other British coalfields, the question of the origin of mountains, stratigraphical considerations, and the faults of the North of England. His object is rather to suggest what he believes to be novel ways of treating the subject than of reaching conclusions or locating limits.

3. On some Phases of the Structure and Peculiarities of the Iron Ores of the Lake Superior Region.' By W. S. Gresley, Esq., F.G.S.

The author has been studying heaps of ore brought from the region lying south-west of Lake Superior since 1890. He describes

rtain structural fea res of the ore-fragments, and discusses the evidences of mechanical movements and chemical alteration exhibited by these fragments.

LV. Intelligence and Miscellaneous Articles. ON ELECTROMAGNETIC TRACTIVE FORCE. BY M. WEBER. The author summarizes the results of his experiments as follows:

(1) An iron wire of great length in comparison with its diameter, one end of which is in a magnetic field parallel to the lines of force, experiences a pull in the direction of its length which for unit area (the square centimetre) of the cross-section is pi=IH=H.

« PreviousContinue »