The author further stated that Presl's genus Bergeria is Carboniferous and not Devonian, and that it has no special affinity with Leptophloeum or Lepidophloios; and he objected to the revival of the name Bergeria. March 26th, 1873.-His Grace the Duke of Argyll, K.T., F.R.S., President, in the Chair. The following communications were read :— 1. "Synopsis of the younger formations of New Zealand." By Capt. F. W. Hutton, F.G.S., of the Geological Survey of New Zealand. In this paper the author gave a summary of the Tertiary and later Secondary formations of New Zealand. He stated that he had been able to determine 375 species of true Mollusca, 12 of Brachiopoda, and 18 of Echinodermata from the Tertiaries; and under each of the formations which he recognizes he gave the number of species of true Mollusca found in it, indicating the number of recent species and of those belonging to other formations occurring in each. He also noticed the range and distribution of the various formations. The Tertiary groups of strata distinguished by the author are, in descending order, as follows:-I. Pleistocene. II. Pliocene: 1, the Newer Pliocene or Whanganui group; 2, the Older Pliocene or Lignite group. III. Miocene: 3, Upper or Arvatere group; 4, Lower or Kanieri group. IV. Oligocene: 5, Upper or Hawke's Bay group; 6, Lower or Waitewata group. V. Eocene: 7, Upper or Ototara group; 8, Lower or Brown-coal group. As belonging to the Mesozoic series, the author also described beds of Danian age, under the name of the Waipara formation. A species of Belemnitella occurs in beds belonging to the Ototara group, and also in the Waipara formation. Volcanic action commenced in the North Island during the deposition of the Waitewata group, and has since been almost continuous in the northern, western, and central parts of the island. In the South Island the volcanic formations appear to belong to the later Cretaceous, Oligocene, and Miocene periods. The volcanic rocks of the Chatham Islands belong chiefly to the Upper Oligocene. 2. "On the Tree Ferns of the Coal-measures, and their relations to other living and fossil forms." By W. Carruthers, Esq., F.R.S., F.G.S. After referring to the remarkably uniform character of the order of Ferns throughout their whole history on the globe, the author pointed out that there existed in the Coal-measures two very distinct kinds of fern-stems, each represented by several species. Both of these were very different from the Chelepteris-group already described by the author in the Journal of the Society. The first group had a stem-structure like that of living tree ferns. In them the vascular elements of the stem formed a closed cylinder round the pith; and the vascular bundles for the leaves were given off from the out-turned edges of the cylinder, where, at regular intervals, corresponding to the position of the leaves, narrow meshes occur for this purpose. To this group were referred the stem described by Lindley and Hutton as Caulopteris Phillipsii, and several hitherto undescribed species from Radstock and Newcastle. No materials had yet been detected which could throw any light on the foliage or fruit of these fern-stems. The second group included some stems the casts of which the author had obtained from Radstock, and the rootstructures from Halifax. By the help of a fine series of specimens in the collections of the British Museum, he was able to correlate the different parts of these plants. The stems had been described by Corda under the name of Stemmatopteris. They differed from the other group chiefly in having the ends of the vascular plates, as seen in the transverse section, turned inwards, and having the bundles of the leaves formed in a complete condition in the axis of the stem. The author showed that the relation of the different parts of the stem in the species of Caulopteris was the same as in a first year's dicotyledon, while in the latter group the analogy of the structures was with the monocotyledonous stem. The roots, which surrounded the older portions of the stem, formed the well-known genus Psaronius of Cotta; and as this was the earlier name, it was proposed to retain it for the genus. There was associated with all the fine specimens of this group which he had received from J. M'Murtrie, Esq., F.G.S., foliage which had been described as Cyatheites arborescens. Although this had not been observed organically connected with the stems, the author adduced several reasons for believing that it belonged to them. If this connexion could be established, it was of the greater importance, as this form was known in fruit, and the fruit established that its affinities were with the living Alsophilas and Cyatheas. Many species of this genus occurred in the continental coalfields; but the author believed that all the specimens found in England, though differing considerably amongst themselves, belonged to a single species. 3. "Notes on the Geology of Kazirùn, Persia." By A. H. Schindler, Esq. In this paper, which accompanied a series of specimens presented to the Museum of the Society, the author described the section presented by the hills in the neighbourhood of Kazirùn. The general surface was described as consisting of nearly unfossiliferous Posttertiary deposits, immediately beneath which is an unstratified marine deposit containing a great abundance of fossils, among which are species of Ostrea, Pecten, and Cidaris (?). Below this deposit is a succession of strata, repeated several times in the hills; and at the bottom of the series in each case is a bed of gypsum. The spaces between the recurrent series are filled up with conglomerates. Beneath the gypseous series is a formation of compact limestone, which rises to a height of about 1500 feet both north and south of the plain of Kazirùn; its beds dip 25°, and their strike is from N.E. to S.W. The author mentioned the occurrence in a gypsum quarry near Kazirùn of three long cylinders from 6 to 10 feet in diameter, composed of the same material as the surrounding rock. He also stated that he had examined several caverns in the neighbouring mountains, and also the great cave at Shahpoor, but without discovering any organic remains. April 9th, 1873.-His Grace the Duke of Argyll, K.T., F.R.S., President, in the Chair. The following communications were read :— 1. "Lakes of the North-eastern Alps, and their bearing on the Glacier-erosion Theory." By the Rev. T. G. Bonney, M.A., F.G.S. The purpose of this paper was to test, by the Lakes of the Salzkammergut and neighbourhood, the theory of the erosion of lakebasins by glaciers, which has been advanced by Professor Ramsay. The author premised: (1) That an extensive glacier could not exist without a considerable area to supply it. (2) That under no circumstances could a glacier excavate a cliff of considerable height (say 1000 feet) approximately vertical. (3) That owing to the proximity of the regions, a theory of excavation which applied to the Western and Central Alps ought to be applicable also to the Eastern Alps. He then proceeded to examine a number of lakes in detail. The Königsee lies in a remarkably deep, steep-sided valley, terminated by a cirque, with cliffs full a thousand feet high, and has no large supply-area behind. The Hallstadtersee is similarly situated, has a cirque at the head, and two lateral valleys nearly at right angles to the lake, up which arms of it have formerly extended. These are not likely to have furnished glaciers which could have excavated the lake; and above the cirque there is no large supply-area. The Gosauthal consists of lake-basins separated by valleys of rivererosion. The Fuschelsee and Wolfgangersee, on the south side of the Schafberg, are separated by a narrow sharp ridge of hills, incapable of nourishing glaciers large enough to grind them out; there are no signs of glaciers from other directions having eroded them. The Mondsee and Attersee (once one lake) on the north lie under the steep cliffs of the Schafberg, which could not have nourished a large glacier; and the ridge of the Schafberg is too sharp to admit of the supposition that a great glacier, coming from the south, has passed over it to excavate the lake; yet the Attersee, in a position least favourable to glacial action, is the largest and deepest lake in the Salzkammergut. The head of the valley in which these lakes lie is really among low hills, in the direction of the Austro-Bavarian plain. The Traunsee was shown to give no evidence in favour of a theory of glacial erosion. Since, then, these lakes either had at their heads preglacial cirques (the very existence of which was incompatible with much erosive power on the part of a glacier), or were beneath sharp and not greatly elevated ridges of rock, the author concluded that they had not been excavated primarily by glaciers. He considered a far more probable explanation to be, that the greater lake-basins were parts of ordinary valleys, excavated by rain and rivers, the beds of which had undergone disturbances after the valley had assumed approximately its present contour. He showed that the lakes were in most cases maintained at their present leveì by drift, and that while in a region so subject to slight disturbances as the Alps positive evidence for his theory would be almost impossible to obtain, no lake offered any against it, and one, the Königsee, was very favourable to it. 2. "On the Effects of Glacier-erosion in Alpine Valleys." By Signor B. Gastaldi. The author described the occurrence in the valley of the Lanzo and other Alpine valleys, at heights between 2000 and 3000 metres (6700 and 10,000 feet), of large cirques, in two of which, in the valley Sauze de Césanne, the bottom was occupied in the autumn by glaciers reduced to their smallest dimensions. The author noticed the various rocks in which these cirques were cut, and expressed his opinion that they are the beds formerly occupied by glaciers, the power of which to excavate even comparatively hard rocks, such as felspathic, amphibolite-, and chlorite-schists, he considered to be proved. The author then referred to the mouths of the Alpine valleys opening upon the plain, which he described as being generally very narrow in proportion to their length, width, and orographical importance; and he pointed out that in the case of the valley of the Stura, at any rate, the outlet of the valley has been cut out by the river. This peculiarity he accounts for by the fact that whilst the calcareous and felspathic rocks are easily disintegrated by atmospheric action, certain other rocks, such as the amphibolites, diorites, syenites, amphibolite-schists, euphotides, serpentines, &c., resist atmospheric denudation; and he indicated the peculiar distribution of these rocks in the region under consideration, by reason of which portions of them occupied the points which are now the mouths of the valleys. XXX. Intelligence and Miscellaneous Articles. ON THE LIMITS OF THE EFFECTIVE POWER OF MICROSCOPES. BY PROFESSOR HELMHOLTZ. ACCORDING to a general law of optical instruments, first ad vanced by Lagrange, the more the magnifying is augmented the narrower become the pencils of rays which pass from a single point of the object through the instrument. The narrower the cones of rays, the less becomes the brightness of the image, and the greater the indistinctness occasioned by entoptic shadows and diffraction. If the magnitude of the smallest perceptible objects is estimated from the distance between each two bright lines which can be recognized as separate from one another, this magnitude may be regarded as equal to that which in the magnified image of the object equals the width of the outer diffraction-fringes of each bright point. This is a quantity dependent only on the angle of divergence of the incident rays, and independent of the construction of the instrument. Calling a the angle formed with the axis by the extreme rays of the pencil from the axial point of the object, incident on and passing through the instrument, at their starting-point, λ the wave-length of the light in the medium in which the object is situated, e the magnitude of the smallest recognizable distance on the object, α €= λ 2 sin a If the rays pass through a plane surface, in air, perpendicular to the axis, and if the values of X and a referred to air be denoted by A and a, we can also write Our newer immersion microscopes make a, nearly equal to a right angle; then e becomes equal to half the wave-length of the light employed. For the middle greenish yellow light of the greatest brightness we can put λ=0·00055 millim., e=0·000275=3636 millim. The more reliable of the newer measurements, especially those made on objects which actually give a broad cone of light, have for their result numbers (as millim., Harting) not much greater than that.-Monatsbericht der kön. preuss. Akad. September and October 1873, p. 625. EXPERIMENTAL RESEARCHES ON NEWTON'S COLOURed rings. BY P. DESAINS. The experimental verification of the theory of Newton's rings. ordinarily consists only in measuring, under one or several incidences, the diameters of a certain number of those rings. A good micrometric screw permits the measurements to be made very conveniently and with much rigour. A screw can also be employed for measuring directly the quantity by which the distance between |