(Engadine) some masses of compact green schist are seen, intercalated in a rather crushed gneiss. They prove to be intrusive dykes modified by pressure. Microscopic examination of specimens from these reveals no trace of any definite structure indicating an igneous rock; a slice, cut from one of the masses within an inch or so of a junction, shows it to be a foliated mass of minute chlorite or hydrous biotite, with granules of epidote (or possibly some sphene) and of a water-clear mineral, perhaps a secondary felspar. An actual junction shows a less distinct foliation and some approach to a streaky structure. A slide from the middle of another dyke (about 18 inches thick) exhibits a more coarsely foliated structure and minerals generally similar to the last, except that it may contain a little actinolite and granules of hæmatite (?) and the clear mineral, in some cases, seems to be quartz. The structure and most of the minerals appear to be secondary. Chemical analysis shows the rock to have been an andesite. A specimen from a third dyke is generally similar, but is rather less distinctly foliated. A somewhat similar, but rather larger intrusive mass by the side of the Lago Bianco shows more actinolite and signs of primary felspar, with other minerals. Here the rock retains some likeness to a diabase. The resemblance of certain of these rocks to somewhat altered sediments is remarkable. The Author considers the bearing of this evidence upon other and larger masses of ' green schist' which occur in the Alps, and expresses the opinion that their present mineral structure may be the result of great pressure acting on more or less basic igneous rocks. 2. The Waldensian Gneisses and their Place in the Cottian Sequence.' By J. Walter Gregory, D.Sc., F.G.S. The lower part of the sequence of the Cottian Alps has been universally divided into three series, of which the lowest has been regarded as a fundamental (basal) Laurentian gneiss. It is the object of the present paper to show that this rock is really intrusive in character and Upper Tertiary in age. The writer endeavours to show this by the following line of argument:-(1) The gneiss consists of only isolated outcrops instead of a continuous band, and these occur at different positions and not always at the base of the schist series; (2) the gneiss is intrusive, because: (a) it includes fragments of the overlying series instead of vice versa, (b) it sends off dykes of aplite into the surrounding schists, (c) it metamorphoses the rocks with which it is in contact, and (d) the schists are contorted near the junction; (3) the gneisses are further shown to be later than the igneous rocks intrusive into the 'pietre verdi' series, as these never traverse the gneiss. No positive opinion as to the age of the overlying schists is expressed in the paper, though it is pointed out that the recent discovery of radiolarian muds in the series may necessitate their inclusion in the Upper Palæozoic. The freshness of the gneisses, the fact that these have not been affected by the early Tertiary Phil. Mag. S. 5. Vol. 38. No. 231. Aug. 1894. R earth-movements, and the absence of authentic specimens of the gneiss in the Cretaceous, Eocene, and Miocene conglomerates, renders their late Tertiary age highly probable. The nature of the contact-metamorphism and the origin of the gneissic structure are discussed, and a classification offered of the earth-movements in the Cottian Alps. February 21st.-Dr. Henry Woodward, F.R.S., President, The following communications were read :— 1. 'On the Relations of the Basic and Acid Rocks of the Tertiary Volcanic Series of the Inner Hebrides.' By Sir Archibald Geikie, D.Sc., LL.D., F.R.S., F.G.S. After an introductory sketch of his connexion with the investigation of the Tertiary volcanic rocks of Britain, the Author proceeds to describe the structure of the ground at the head of Glen Sligachan, Skye, which has recently been cited by Prof. Judd as affording inclusions of Tertiary granite in the gabbro, and as thus demonstrating that the latter is the younger rock. He first shows that the gabbro, instead of being one eruptive mass, consists of numerous thin beds and sills of different varieties of gabbro, some of which were injected into the others. These various sheets, often admirably banded, can be seen to be truncated by the line of junction with the great granophy re-tract of Glen Sligachan. A large mass of coarse agglomerate is likewise cut off along the same line. These structures are entirely opposed to the idea of the gabbro being an eruptive mass which has broken through the granophyre. They can only be accounted for, either by a fault which has brought the two rocks together, or by the acid rock having disrupted the basic. But there is ample evidence that no fault occurs at the boundaryline. The granophyre becomes fine-grained, felsitic, and spherulitic along its margin, where it abuts against the complex mass of basic rocks. These structures continue altogether independent of the varying distribution of the gabbros, and are seen even where the granophyre runs along the side of the agglomerate. Similar structures are of common occurrence along the margins of the granophyre-bosses and sills of the Inner Hebrides, being found not only next the gabbro, but next the Jurassic sandstones and shales. They are familiar phenomena of contact in all parts of the world, and are sufficient of themselves to show that the granophyre of Skye must be later than the gabbro. The Author then describes three conspicuous dykes, from 8 to 10 feet broad, which can be seen proceeding from the main body of granophyre and cutting across the banded gabbros. One of these is traceable for more than 800 feet in a nearly straight line. The material composing these dykes is identical with that constituting the marginal portion of the granophyre-mass. It presents the most exquisite flow-structure, with abundant rows of spherulites. The Author exhibited a photograph of one of the dykes ascending vertically through the gabbros. Numerous dykes and veins of the same material, not visibly connected with the main granophyremass, traverse the gabbros of the ridge of which Druim an Eidhne forms a part. Some of these are described in the paper, and it is shown that the flow-structure follows the irregularities of the gabbro-walls and sweeps round enclosed blocks of altered gabbro. The inclusions' described by Prof. Judd are portions of these dykes and veins. There is not, so far as the Author could discover, a single granite-block enclosed in the gabbro anywhere to be seen at this locality. He therefore claims not only that his original description of the relations of the rocks was perfectly correct, but that the evidence brought forward to contradict it by Prof. Judd furnishes the most crushing testimony in its favour. 2. 'Note on the Genus Naiadites, as occurring in the Coal Formation of Nova Scotia.' By Sir J. William Dawson, K.C.M.G., LL.D., F.R.S., F.G.S. With an Appendix by Dr. Wheelton Hind, B.S., F.R.C.S., F.G.S. March 7th.-Dr. Henry Woodward, F.R.S., President, The following communications were read :— 1. The Systematic Position of the Trilobites.' By H. M. Bernard, Esq., M.A., F.L.S., F.Z.S. 2. Landscape Marble.' F.C.S. By Beeby Thompson, Esq., F.G.S., The Cotham Stone is a hard, close-grained, argillaceous limestone with conchoidal fracture. The dark arborescent markings of the stone rise from a more or less stratified dark base, spread out as they rise, and terminate upwards in wavy banded portions of the limestones. In some specimens two landscapes' are seen, one above the other, each rising from a distinct dark layer. The Author describes the microscopical and chemical characters of the rock, and its mode of occurrence, and discusses the explanations which have been put forward to account for its formation, especially that of Edward Owen, who in 1754 gave the first published description of the Cotham Stone, and that advanced by Mr. H. B. Woodward in the 'Geological Magazine' for 1892. He then proposes a new explanation to account for the formation of the rock, and maintains that its peculiar characters are due to interbedded layers of vegetable matter, which decomposed and evolved carbonicacid gas and marsh-gas. This decomposition continued while several inches of new sediment were laid down, the result being that arborescent markings were produced along the lines taken by the escaping bubbles, and that the upward pressure of these gases, after their escape had been prevented by increasing coherence or greater thickness of the upper layers of sediment, caused the corrugations in the upper surface of the stone. He further discusses the composition of the stone, and describes experiments which he made to illustrate his views. 3. On the Discovery of Molluscs in the Upper Keuper at Shrewley, in Warwickshire.' By the Rev. P. B. Brodie, M.A., F.G.S. March 21st. Dr. Henry Woodward, F.R.S., President, The following communications were read: 1. On the Origin of certain Novaculites and Quartzites.' By Frank Rutley, Esq., F.G.S., Lecturer on Mineralogy in the Royal College of Science, London. The novaculites of Arkansas have already been admirably described by Mr. Griswold in vol. iii. of the Arkansas Survey Report for 1890. One of the characteristic microscopic features in Ouachita stone is there stated to consist in the presence of numerous cavities, often of sharply-defined rhombohedral form, which Mr. Griswold considers to have been originally occupied by crystals of calcite or dolomite. The Author, while admitting that the cavities were no doubt once filled by the latter mineral, ventures to differ from Mr. Griswold, and some of the authorities he cites, concerning the origin of the rock. Crystalline dolomites, when dissolving, become disintegrated into minute but well-formed rhombohedra. As the process of dissolution proceeds these crystals may become so eroded that the rhombohedral form is no longer to be recognized. The Author points out that no inconsiderable proportion of the cavities in Ouachita stone present irregular boundaries, such as the moulds of partially eroded rhombohedra would show. He then offers a fresh interpretation of these cavities, so far as the origin of the rock is concerned : 1st. He assumes that beds of crystalline magnesian limestone have been slowly dissolved by ordinary atmospheric agency and the percolation of water charged with carbonic acid or other solvent. 2nd. That, as the limestone was being dissolved, it was at the same time being replaced by silica, which enveloped minute isolated crystals and groups of crystals, some perfect, others in various stages of erosion. 3rd. That the silica assumed the condition of chalcedony, its specific gravity, as stated by Mr. Griswold and as determined by the Author, being low in comparison with that of quartz. 4th. The residuum of the original dolomite or dolomitic limestone was removed, leaving the perfect and imperfect rhombohedral cavities. A calciferous, gold-bearing quartzite from the Zululand goldfields is described and a similar origin is ascribed to it, but in this case the original rock appears to have been simply a limestone, not a dolomite. The gold seems to occur chiefly in the calcareous portions of the rock. The Author has also been tempted to suggest a similar origin for the saddle-reefs of the Bendigo gold-field. In all of these cases the train of reasoning is based upon the conclusions arrived at in his previous paper On the Dwindling and Disappearance of Limestones.' He indicates that the stratigraphical relations of the Arkansas novaculites, as described in Mr. Griswold's Report, are such as to warrant the assumption that limestones once occurred in the position now occupied by beds of novaculite. Many collateral matters are dealt with in the paper which cannot be given in abstract: among them is an attempt to classify quartzites. 2. Note on the Occurrence of Perlitic Cracks in Quartz.' By W. W. Watts, Esq., M.A., F.G.S. The Author of this communication described some specimens of the porphyritic pitchstone of Sandy Braes in Antrim, which are deposited in the Museum of Science and Art in Dublin, and in that of Practical Geology in Jermyn Street. They exhibit admirable examples of perlitic structure in the brown glassy matrix and the presence of polygonal, circumferential, and radial cracks is noticed. The porphyritic crystals of quartz are traversed by curved fissures of retreat, not so perfect as those found in the glass, but better than those usually produced by the rapid cooling of Canada balsam. The fissures in the quartz are frequently prolonged into the matrix, undergoing only a very slight and almost imperceptible deviation in direction at the junction. But in addition to this the quartz is often found to act as a centre of strain, the inner cracks of the perlite being wholly in quartz, the next traversing both, and the outer ones in glass only. In other examples the outer cracks of a matrix perlite sometimes enter the quartz, while in others polygonal cracks occur, and join up in, the quartz and give off radial cracks precisely like those of the matrix. These observations lead to the conclusion that the quartz and glass must have contracted at about the same rate, and that the observation of perlitic structure in a rock with trachytic or felsitic matrix by no means proves that the rock is necessarily a devitrified glass. References are given to somewhat similar observations by Fouqué and Michel-Lévy, and by Iddings. I XXVII. Intelligence and Miscellaneous Articles. ON THE THERMAL BEHAVIOUR OF LIQUIDS. To the Editors of the Philosophical Magazine. HAVE been prevented for a considerable time from attending to my usual studies by serious domestic trouble, and thus I was not able at once to read and consider the observations of Professors |