members of the volcanic series,' and that 'there is no true passage of the sedimentary rocks into it; on the contrary, the conglomerates which abut against it are in great part made out of its fragments, so that it must have been already in existence before these Cambrian strata were deposited.' The grits and slates which overlie the conglomerates in these areas have always been classed by the Geological Survey as the Lowest Cambrian; therefore any attempt to extend the term Cambrian so that it might include the much older rocks which the surveyors had incorrectly marked as intrusive, and chiefly of Lower Silurian age,' the author thinks is unwarrantable. The error which caused the surveyors to class other pre-Cambrian rocks as 'altered Cambrian' equally renders it impossible to group these with the Cambrian, especially as in no instance has it been shown that the so-called 'altered Cambrian rocks' have their equivalents amongst the unaltered Cambrian rocks of the Survey. Moreover, it is certain that there is a marked unconformity at the base of the Cambrian (unaltered Cambrian of the Survey) in all the areas in Wales where the beds are seen to rest on the rocks classed by the author and others as of pre-Cambrian age. 11. On the Reptilia of the British Trias. By E. T. NEWTON, F.R.S. This communication is a review of our knowledge of the reptiles which have been recorded from the Triassic strata of Britain. In the first place attention is called to the teeth from Durdham Down, Bristol, described by Riley and Stutchbury in 1836 under the generic names of Palaosaurus and Thecodontosaurus, which, with additional specimens, were further described by Professor Huxley in 1869, he regarding them both as dinosaurian. The two genera are distinguished by the form of their teeth. Closely allied to Palæosaurus is the tooth described by Murchison and Strickland in 1837 as Megalosaurus, but subsequently named Cladyodon by Owen. Another and still larger tooth, from the same neighbourhood, has been referred by Professor Huxley to Teratosaurus (= Zanclodon): it is very similar to that of Cladyodon, but is more compressed, and has both anterior and posterior edges serrated to the base. Rhynchosaurus articeps, from the Keuper of Grinshill, Shropshire, was described by Owen in 1841 from a skull, but was further illustrated by additional specimens, including other parts of the skeleton, described by Professor Huxley in 1887. This form, which is allied to the recent Sphenodon, is also near to the Hyperodapedon, remains of which have been found in the Elgin Sandstone and also in the Trias of Warwick and Devon. Hyperodapedon was made known by Professor Huxley in 1858, but first described it in 1869, and more fully in 1887 from a fine example now preserved in the British Museum. Telerpeton Elginense, the celebrated lizard of the Elgin Sandstone, was found in 1850 by Mr. Patrick Duff, and described by Dr. Mantell in 1851 as having amphibian affinities. Additional examples were, however, described by Professor Huxley in 1867, who showed that its affinities were with the lacertilia, and not with the amphibia. Telerpeton is probably closely related to the living Sphenodon. Stagonolepis Robertsoni was really the first reptile found in the Elgin Sandstone; a series of scutes from Lossiemouth being thus named by Agassiz just fifty years ago (1843), but were thought by him to be the scales of a fish. The reptilian nature of this fossil was shown by Professor Huxley in 1858, and more abundant material has been described by the same writer in 1875 and 1877, which has established the crocodilian affinities of this Triassic reptile. Dasygnathus longidens is the name suggested by Professor Huxley for a jaw with long teeth from the Elgin Sandstone, which had at first been referred to Stagonolepis. This form Professor Huxley thought might be dinosaurian, but additional information is much wanted to establish its true affinities. The dicynodont remains, noticed by the present writer at the meeting of this Association last year at Edinburgh, have now been worked out, and the results, fully illustrated, will shortly appear in the Phil. Trans.' of the Royal Society. Four forms nearly allied to Dicynodon have been named Gordonia Traquairi, G. Huxleyana, G. Duffiana, and G. Juddiana. Another dicynodont more nearly related to the Ptychognathus of Owen, but with a short muzzle and no teeth, has been named Geikia Elginensis. The peculiar horned reptile, resembling the Moloch lizard, but apparently most nearly related to the South African Pareiasaurus, has been named Elginia mirabilis. Work among the Elgin reptiles is still going on, and two entirely new forms are now made known for the first time. One of these was found by Mr. James Grant, of Lossiemouth; and, although the exact locality is uncertain, there is no doubt as to its being from the sandstone of the Elgin area. This specimen, which includes the skull (about three inches long) and the front part of the trunk, is evidently related to Stagonolepis. The second new form was obtained by the Rev. Dr. Gordon from the Elgin Sandstone of Spynie Quarry, and will eventually be preserved in the British Museum. With the exception of the fore limbs and neck, nearly the whole of the skeleton has been preserved. Much of the skull has been very successfully cleared from the matrix by Mr. Richard Hall, of the British Museum, and was exhibited at a soirée of the Royal Society, when its resemblance to Aëtosaurus was pointed out by Mr. Arthur Smith Woodward. This reptile is of much interest, as it seems to be a form intermediate between the crocodiles and dinosaurs, being, apparently, related on the one hand to the Parasuchia and on the other to the theropodous dinosaurs. The skull is, in fact, that of a miniature megalosaur. FRIDAY, SEPTEMBER 15. The following Papers and Reports were read:— 1. A joint Discussion with Section E on the Limits of Geology and 2. The Dissected Volcano of Crandall Basin, Wyoming. The writer in exploring the north-eastern corner of the Yellowstone National Park and the country east of it came upon evidences of a great volcano which had been eroded in such a manner as to expose the geological structure of its basal portion. The work was carried on as a part of the survey of this region under the charge of Mr. Arnold Hague, of the United States Geological Survey. This paper is an extract from a chapter in the final report on the Yellowstone National Park in process of completion, and the writer is indebted to Major J. W. Powell, Director of the Survey, and to Mr. Hague, chief of the division, for permission to present it at this time in anticipation of the publication of the final report. The area of volcanic rocks described is but a small portion of the great belt of igneous material that forms the mountains of the Absaroka range, lying along the eastern margin of the Yellowstone Park. The volcano of Crandall Basin is one of a chain of volcanic centres situated along the northern and eastern borders of the Yellowstone Park, which are all distinguished by a greater or less development of radiating dikes, and by a crystalline core eroded to a variable extent. The Paleozoic and Mesozoic strata which formed an almost continuous series to the coal-bearing Laramie had been greatly disturbed, and almost completely eroded in places, before the volcanic ejectamenta in this vicinity were thrown upon them. The period of their eruption is therefore post-Laramie, presumably early Tertiary. The first eruptions of andesite were followed by those of basalt in great quantities, and these by others of andesite and basalt like the first. This was succeeded 1893. 3 с by a period of extensive erosion, reducing the country to nearly its present form. Then came the eruption of a vast flood of rhyolite constituting the Park plateau, which was followed in this region by smaller outbreaks of basalt. The last phase of volcanic activity is found in the geysers and fumaroles which have rendered the region famous. The volcano of Crandall Basin consists chiefly of the first series of basic andesites and basalts. The earliest acid andesite which occurs beneath these rocks appears to be the remnant of eruptions from neighbouring centres. Nothing remains of the original outline of the volcano. The district is now covered by systems of valleys and ridges of mountain peaks that rise 2,000 to 5,000 feet above the valley bottoms. The geological structure of the country, however, makes its original character evident. The outlying portions of the district to the south, west, and north consist of nearly horizontally bedded tuffs and subaerial breccias of basic andesite and basalt. With these are intercalated some massive lava flows, which are scarce in the lower parts of the breccia, but predominate in the highest parts above an altitude of 10,000 feet. Here they constitute the summits of the highest peaks. In contrast to the well-bedded breccias around the margin of the district the central portion consists of chaotic and orderless accumulations of scoriaceous breccia with some massive flows. These breccias carry larger fragments of rock and exhibit greater uniformity in petrographical character. A still more noticeable feature of the central portion of the district is the occurrence of dikes, which form prominent walls, and may be traced for long distances across the country. The greater number of them are found to converge toward a centre in the highest ridge in the middle of the drainage basin of Crandall Creek. A small number converge towards a second centre three or four miles east of the first. In the southern part of the district there are many dikes trending towards a centre near the head of Sunlight Basin, about fifteen miles south of the Crandall centre. The centre towards which the Crandall dikes converge is a large body of granular gabbro graduating into diorite. It is about a mile wide, and consists of numerous intrusions penetrating one another, and extending out into the surrounding breccia, which is highly indurated and metamorphosed in the immediate vicinity of the core. Within the area of indurated breccia the dike rocks become rapidly coarser-grained as they approach the gabbro core. This was undoubtedly the central conduit of an ancient volcano, the upper portion of which has been eroded away. Upon comparing the geological structure of this region with that of an active volcano like Etna it is apparent that the lava flows which form the summits of the outlying peaks must have been derived from lateral cones fed by dikes radiating from the central conduit; and assuming that the volcano of Crandall Basin was similar in type to that of Etna, an idea of its original proportions is derived by constructing upon profile sections through the Crandall core the outline of Etna. If the erosion of the summits of the highest peaks is neglected the resulting height of the ancient volcano above the limestone floor is estimated at 13,400 feet. This is undoubtedly too low, and is well within the limits of present active volcanoes. Erosion has removed at least 10,000 feet from the summit of the mountain to the top of the high central ridge in which the granular core is situated, and has cut 4,000 feet deeper into the valleys on either side. It has prepared for study a dissected volcano, which, it is hoped, will in time reveal some of the obscurer relationships existing between various phases of igneous rocks. 3. On Structures in Eruptive Bosses which resemble those of ancient While it is now the general belief of geologists that the older granitoid and banded gneisses were originally eruptive masses, considerable difference of opinion exists as to the cause of the peculiar and characteristic structure which distinguishes gneiss from ordinary amorphous eruptive material. The pregnant sugges tion of Lehmann that this structure is essentially due to mechanical deformation has been widely accepted, and has undoubtedly been of great service in the investigations of the last ten years among pre-Cambrian rocks. That the foliation of many gneisses has arisen from the effects of enormous compression can no longer be disputed. But among these rocks other structures occur which cannot be satisfactorily so explained. In the granulitic gneisses, where the folia are thin, and where over considerable spaces a marked uniformity of lithological character prevails, crushing and recrystallisation have no doubt played a chief part in the production of the gneissic structure. But in the coarsely banded varieties, where thick layers of different chemical and mineralogical composition alternate irregularly with each other, mechanical deformation seems to be wholly inadequate to account for this arrangement. The author stated that he had pointed out some years ago that a close analogy might be traced between this banded character and certain structures to be observed in the deeper portions of large intrusive bosses. He had since then had opportunities of repeating and extending his observations, which had led him to the belief that the coarsely banded arrangement in the ancient gneisses was not due to any subsequent crushing and recrystallisation, but was a structure developed in the original, massive, or eruptive rock before its final consolidation. In the deeper-seated parts of intrusive bosses he had noticed that the component minerals had sometimes been segregated in parallel bands, each of which was marked by the predominance of one of them, and that the minerals had there crystallised in much larger forms than in the main body of the rock. Layers of felspar, pyroxene, olivine, and iron ores had in this way been separated out, and could be traced in alternate parallel bands for distances of many yards, sometimes even exhibiting puckered, folded, and inverted structures. Such segregations were so like the hornblendic, felspathic, quartzose, and pyroxenic bands of many gneisses that the observer could hardly at first believe that they were not portions of some ancient rock enclosed within the eruptive boss. He could soon convince himself, however, that they were really integral parts of the general mass. Not only is the banded structure of the gneisses perfectly reproduced in the bosses, but another equally characteristic structure, that of the pegmatite veins, is likewise simulated. Occasionally veins of this nature composed of the same minerals as the boss, but aggregated in different proportions, may be seen, not only in the main amorphous mass of the rock, but even traversing the segregated bands. So closely does this association of structures resemble that of the old gneisses as to impress the conviction on the observer that it probably represents the origin of some of the most conspicuous features in these rocks. Illustrations of the structures described may be found in eruptive bosses of Palæozoic age, but the best examples which the author has seen occur among the Tertiary gabbros of the Western Isles. 4. On the Pittings in Pebbles from the Trias. The singular indentations in the pebbles of the pebble beds of the Trias have been variously attributed to solution and pressure, and in limestone pebbles Sorby has conclusively shown how both have shared in their formation. No one, however, appears to have suggested the influence of slight movements as a powerful adjunct to pressure; and yet earth tremors are of such constant occurrence that slight movements must exist. How great may be the influence of these is proved by the incised bones of the great Irish deer, which have made sharp and deep cuts into each other wherever they have happened to lie in contact, and this although only under the pressure of a peat bog. Still better illustrations are afforded by some pebbles, to which my attention has been directed by my colleague Mr. MacHenry. These are from an ancient beach over which the tram line passes Tritonville, Sandymount: they are covered with impressions essentially similar to those on the Trias pebbles, a result of the perpetual jarring produced by the passing trams. It is obvious that under the great pressure to which the Trias pebble beds have been exposed the slightest trembling at points of contact would produce similar or even more marked effects. at 5. On Bones and Antlers of Cervus giganteus incised and marked by Mutual Attrition while buried in Bogs or Marl. By V. BALL, C.B., LL.D., F.R.S. From time to time bones and antlers of this extinct deer have been found with peculiar cuts and marks upon them, which have suggested to some observers the work of man; careful examination has shown, however, that these cuts and polished and indented surfaces are all really due to the same cause, namely, the sawing or rubbing together of bones and antlers as they lay in contact while embedded in marl underlying peat. We cannot say with any degree of certainty what the cause of the movement may have been. It may perhaps have been due to alternate expansion and contraction, up and down, according to the amount of moisture in the bog; possibly, however, it was connected with earth-tremors, the origin and extent of which cannot be so easily explained. The several finds of these cut bones, of which examples were exhibited to the Section, were made at Legan, five miles south of Edgeworthstown, Co. Longford; and on the left bank of the river Camoge, one mile from Lough Gur, and close to Kilcullen House, Co. Limerick. In the former case, which was described by Professor Jukes in the year 1863, the bones lay in shell marl 2 or 3 feet thick, resting on blue clay (drift) and covered by 15 feet of peat; but originally, before being cut, the peat had been 50 feet thick at this spot. In the Lough Gur locality, which is described by Dr. Carte, the mode of occurrence of the bones was similar. 6. On a Mass of Cemented Shells dredged from the Sea Bed. 7. Note to accompany the Exhibition of a Geological Map of India. By R. D. OLDHAM, A.R.S.M., F.G.S., of the Geological Survey of India. Two maps are exhibited, on the scales of 96 and 32 miles to the inch respectively. The smaller is a chromo-lithograph, and will be published shortly with the second edition of that portion of the 'Manual of the Geology of India' which deals with the stratigraphical and structural geology of the Empire. The larger is a manuscript map representing in greater detail the state of our knowledge of Indian geology at the end of 1892. It is well known that the Indian Empire is divisible into three geological regions, which are recognised as (1) the Peninsular, (2) the extra-Peninsular, and, separating them, (3) the Indo-Gangetic alluvium. It is in the extra-Peninsular region that most of the additions to our knowledge of Indian geology have been made since the publication of a general map with the first edition of the 'Manual of the Geology of India.' The most important of these additions, so far as the area coloured goes, are in Upper Burma and the country explored by my colleague Mr. Griesbach while attached to the Afghan Boundary Commission; but, besides actual additions to the coloured area, great additions have been made to our knowledge of the stratigraphy and correlation of the rocks within the area which was coloured on the previous map. Among the most important stratigraphical features of the extra-Peninsular area may be ranked the fine development, and abundant fossils, of the Lower Trias of the Central Himalayas; the rich fauna of this period, very scantily represented in Europe, is now under description, and the publication of the results must be looked forward to as an important addition to geological knowledge. Another feature is the very fine development of Cretaceous and Tertiary beds on the western frontier, and here the main stratigraphical break is not between the Cretaceous and Tertiary, but at the base of the Lower Cretaceous of accepted chronology. Structurally the most important feature of the extra-Peninsular area is the great disturbance the beds have undergone, a disturbance which has taken place |