Both of these observers agree in regarding certain breccias occurring at the mouths of the rivers Otter and Sid as the base of the Keuper, the former of which the author accepts. The latter is explained as being the same breccias again brought up by the fault at the Chit Rock. The writer regards the Sid section as on a far higher horizon than the Otterton one for the following reasons:-The Otterton breccias are overlaid by a great thickness of sandstones seen between Otterton Point, Ladrum Bay, the base of High Peak Hill, and even further east. The fault at the Chit Rock only brings up the upper portion of these sandstones, the highest portions of which are continued to the east side of the Sid. The alleged river Sid breccias here have no occurrence; they are only the uppermost beds of the red nobbly or concretionary-like sandstones which are almost immediately overlaid by the Keuper marls. Between these alleged Sid breccias and the Otterton breccias there should intervene about 150 feet or more of the mottled or current-bedded sandstones seen in the localities already referred to. TUESDAY, SEPTEMBER 15. The following Papers were read:— 1. On the Disturbance of Junction Beds from Differential Shrinkage and similar Local Causes during Consolidation. By G. W. LAMPLUGH, F.G.S. Upon returning to the investigation of comparatively undisturbed Mesozoic strata after having studied distortion-structures produced by earth-movement in Older Palæozoic rocks, the author's attention has been frequently arrested by local disturbances of the original bedding which cannot be assigned to the agency of deep-seated earth-movement, but are clearly due to minor stresses arising from some local cause in tracts limited in extent both horizontally and vertically. These disturbances are most noticeable where thin bands of one kind of material are imbedded in thick deposits of another kind, and along the junctions where thick masses of different lithological character occur in stratigraphical sequence. Examples of the first-mentioned condition are abundant in the Hastings beds of the Wealden formation, where thin layers of clay or shale interbedded with thick sands and sandstones are often disrupted into irregular patches and partly mixed with the enclosing sands. The second condition is frequently illustrated in junctions of the Lower Greensand with underlying clays, where strips have been torn from the irregular surface of the clay and dragged up for a few inches into the sands, as was seen in the recently widened railway cutting at Redhill and in the pit-sections at the Dover Colliery. Similar effects have often been supposed to denote the breaking-up of the surface below the junction by erosive agencies, but this explanation is rarely adequate. While some of these local disturbances may have been caused by unequal loading within limited basins of sedimentation, in the manner discussed by E. Reyer, the author is of opinion that in most cases they may be assigned to local stresses resulting in part from the differential contraction of sediments of diverse composition while losing their water of sedimentation, and in part from their unequal yielding under equal superincumbent load. Masses of peat, sand, clay and calcareous sediments accumulated under normal conditions must pass from the wet state to the consolidated or partly consolidated state with different time-rates and with different physical results; and we may expect to find signs of local tension and readjustment along the boundaries of such masses. In thick wedges of strata which thin out rapidly, as, for example, in the K. K. Geol. Reichsanstalt Wien; Jahrbuch, xxxi, 1881, pp. 431-444. Triassic rocks of many localities and the Wealden and Lower Greensand of the south of England, differential shrinkage may be responsible for many of the smaller vertical displacements by which the beds are readjusted. Faults are sometimes found to dwindle and die out downward, and in certain cases these may be explicable as the result of unequal contraction in masses of irregular thickness. 2. On some Contorted Strata occurring on the Coast of Northumberland, By J. G. GOODchild, 3. Some Facts bearing on the Origin of Eruptive Rocks. The author exhibited a number of photographic slides in order to demonstrate that intrusive masses, as a rule, replace their own volume of the rocks they invade and do not cause displacement to any important extent. Hughes, and also Clough, had already published evidence to the same effect. Several of the hand-specimens that had been photographed were exhibited at the Meeting. In the course of nearly forty years' field experience he had never met with any intrusive rock whose mode of occurrence could not be explained by the theory that the rocks in question had been substituted for those whose place they had occupied. The older rocks had, obviously, been gradually removed, and the newer ones had been, concurrently, left in their place. He thought that it was only in those cases in which the pressure to be overcome had been below a certain (unknown) amount that actual displacement occurred. This might happen where a viscid magma was being forced into the loose materials in the outer parts of a volcano. These, however, are the parts of a volcano which rarely survive subsequent geological changes. The mode of attack of the erosive magma was next illustrated by a series of views representing various unfinished stages in the process. These demonstrated that the intruding magma ate its way along any divisional planes in the rock invaded, and by physico-chemical processes the advancing wedges enlarged and extended forward, solely by peripheral solution, which ended by surrounding the part attacked by the fluid magma, and thus permitting the detached portions to float into the trunk stream. Further stages in the process of mastication, digestion, and assimilation were shown by other slides, as well as by specimens exhibited at the Meeting. Three or four slides of pseudo-dykes and sills were shown. These occur within fragmentary materials of volcanic origin. He considered that these clastic rocks had been softened in place and had subsequently reconsolidated in the massive form without change of position. Finally, to account for the facts, he advanced the hypothesis that the chief agent concerned in bringing about these changes was water operating under pressure and at a moderately high temperature, in which were held in solution the substances dissolved in sea-water. These underwent concentration by the action of volcanoes, and in that state were competent not only to dissolve the constituents of rocks, but to add to sedimentary or other rocks the substances in which their composition is deficient as compared with that of the eruptive rocks. Slow diffusion and a circulatory movement of the whole magma equalised the composition of the compound. He thought that the sedimentary rocks thus affected could furnish the materials for those rocks in which felspar containing lime and soda predominate, while the acid series might have arisen in like manner from the solution of the granitic foundation of the Earth's Crust. 4. On a Possible Cause of the Lethal Effects produced by the Dust emitted during the Recent Volcanic Eruptions in the West Indies. By J. G. GOODCHILD. When volcanic materials are expelled into the air in the form of either lavs streams or ejected fragments, some of their component minerals may be in a chemical state in which they are capable of combining with a higher percentage of oxygen than they contained when they left the volcanic vent. Two results would follow from such oxidation-one being the rise of temperature due to the heat of combination. the other, correlative to it, an abstraction of oxygen from the surrounding atmosphere proportionate in amount to the surface acted upon. In the cases in which a large quantity of finely divided material in a more or less pumiceous state is suddenly discharged into the air the aggregate surface exposed to the atmosphere must be extremely large, and it appears likely that a quantity of oxygen proportionately great may be abstracted. The loss of oxygen is, of course, soon made good by diffusion from the areas around; but, for the time being, it appears possible that the air carried forward along with heavy discharges of volcanic dust, such as were ejected during the late eruptions in the West Indies, may have sustained their initial temperature for some time through oxidation, and may consequently have raised the temperature of the surrounding air to s very high point. Furthermore, the abstraction of so large a quantity of oxygen may have also helped to make the air around the stream of dust unsuitable for the support of life, 5. Notes on the Metalliferous Deposits of the South of Scotland. 6. Notes on the Glacial Drainage of the Forest of Rossendale. 7. A Theory of the Origin of Continents and Ocean Basins. Whatever the conditions at present obtaining in the interior of the earth, it is naturally supposed to have originally passed through a stage in which the conditions would be represented by a solid, or potentially solid, nucleus, a slowly forming and slowly thickening acid crust, with a liquid and more or less basic interstratum. At first the crust would be sufficiently flexible to accommodate itself to the tidal movements of the subjacent liquid interstratum, but when it became too rigid to admit of this tidal movement it would be broken up, the fracture probably following certain fairly defined and assignable lines. It is argued that the fragments would not have gone under,' but would have remained with their surfaces at a considerably higher level than the surface of the magma, and have become so fixed by consolidation of the magma around them. It is suggested that the first great breach in the crust followed the outline of the tidal protuberance, and was, in all probability, effected at some conjunction of the sun and moon with cataclysmal suddenness, the intervening crust being shivered into small fragments, these fragments being subsequently disposed of by fusion in and incorporation with the magma. The first oval breach thus caused is the prototype of the Pacific Ocean. Further fractures, along definite lines, gave rise to the other oceans, and caused the separation of the continents. Under the influence of tidal retardation the fragments as thus blocked out became separated and finally moored at their respective distances by the solidification of the magma around them. With the resolidification of the crust, a series of stresses is set up between the ocean basins, which consist of the more basic, consequently specifically heavier, more quickly conducting material, and the more acid, specifically lighter, more slowly conducting continental masses. The former are, in consequence of their character and composition, the more stable portions of the resolidified crust. Further, cooling therefore leads to their sinking down on the cooling and shrinking nucleus, and their elbowing aside of the continental masses, which come to be elevated in lines parallel to and extending along their margins. With further cooling the superficial layers of the continents are thrown into folds and overfolds, which would tend to find relief along the ocean margins and the central axis of the Old World by over-thrusting of these layers. Central uplifts in the continental areas may also have resulted from such pressure. The tendency of the ocean to become deeper and the continent to become more elevated as time goes on, leads more and more to the withdrawal of the waters of the ocean (which might at first almost or altogether have covered the continental areas) from these areas, and hence to greater and greater restriction in the limits of the areas of deposit as traced from earlier to later geological times. The origins of the Mediterranean and of the central axis of the Old World are directly deduced from theory, and the unequal distribution of land and sea in the northern and southern hemispheres is also brought into line with it. Though the contraction of the ocean basins has been the main cause of the deformation of the crust, the contraction of the continental areas has also had some share in the result. The central ridge of the Atlantic bottom may be an earth fold caused by pressure of the contiguous continental masses; but it may also be due to longitudinal fissures permitting volcanic action and consequent accumulation of volcanic products, the fissures in such case marking the relief of tension arising from the same cause. The formation of secondary ridges parallel to the oceano-continental margins but at some distance towards the continental side, seems to have played an im portant part in the evolution. Extending oceanwards in their operation they appear in some instances to have raised up portions of the ocean bottom into continuity with the land surface. In this way, with the aid of volcanic action, the ocean basins appear, in not a few instances, to have been successfully bridged. As the permanency of the master-features of the globe in much their present form is a necessary corollary of the theory, such bridging of the ocean basins also becomes a necessary part of the theory, and is fairly met on the lines indicated. Explaining as it does the general outlines of continents and ocean basins, as well as a large number of facts both in geography and geology, it is contended that the theory as sketched does represent in a general way the actual process by which the permanent features of the globe took origin. WEDNESDAY, SEPTEMBER 16. The following Report and Papers were read: 1. Report of the Committee on Changes in the Sea Coast of the United Kingdom.-See Reports, p. 258. 2. Notes on the Sarsen Stones of the Bagshot District. The blocks of sandstone or quartzite known as Sarsen Stones are found in many parts of the south of England. They occur at or near the surface of the ground, as well as in or at the bottom of the gravels. They are usually believed to be derived from the Bagshot or Reading Beds, but there does not seem to be definite evidence of the discovery of a Sarsen Stone in situ in these or in any other formation. Probably the best-known examples are the great stones which form the outer circle at Stonehenge. Sarsens are, however, frequently to be seen as gate-posts or corner-stones, and in some districts they have been used as building stone to a considerable extent. Sarsens are very abundant in the neighbourhood of Bagshot. They have been observed by the author firstly, and most frequently, at the bottom of or close to the bottom of beds of gravel; secondly, and rather less often, at or near the surface of the ground where there is no gravel; and thirdly, but only seldom, in gravel some height above the bottom of the gravel. The author has never seen a Sarsen Stone in situ, for though he has seen many partially uncovered stores, they have in every case shown signs of wear by either water or weather. At the same time he has noticed that the corners are frequently angular, and many of the stones have been very slightly worn and certainly not rolled by water currents or streams. The country around Bagshot is formed of the Bagshot Beds, largely of Upper Bagshot Beds, which are shown by their fossils to be of Lower Barton age, and the author suggests that soon after their deposition this part of England rose somewhat above sea-level, and remained as a wide, fairly level, and low-lying flat covered with marsh and vegetation for a very long period. The Sarsen Stones are, he believes, indurated portions of this old land surface. If this is correct, it accounts for all the above-mentioned facts, and also for the presence of numerous rootlet tubes in the Stones, and for the absence of marine shells or of casts thereof. If after a long period of repose an elevation of the land took place, the streams would rapidly cut channels in the sandy soil and leave the indurated fragments of the old surface scattered about at various levels, and many of these would become buried in the beds of gravel, thus accounting for the presence of the Sarsen Stones in the gravels. It was suggested long ago by Mr. Hudleston that the concretionary action which formed the Sarsens was due to the decomposition of vegetable matter, and a somewhat similar opinion has been expressed by the Rev. Dr. Irving.1 3. On the Occurrence of Stone Implements in the Thames Valley between Reading and Maidenhead. By LLEWELLYN TREACHER, F.G.S. Many neolithic celts have been obtained from the gravel of the bed of the present river at Tilehurst, Bourne End, and Maidenhead, but few at any inter vening place. Surface finds are also more numerous in those localities than anywhere else in the district. There may have been fords or hunting resorts at these places in neolithic times, and the axe-heads may have been lost in the stream. Paleolithic implements have been found abundantly in terrace gravels at heights of from 60 to 120 feet above the river on both sides of the valley. The places where they occur in greatest numbers are near Caversham, 115 feet; Grovelands, Reading, 75 feet; Sonning, 95 feet to 60 feet; Ruscombe, 60 feet; Cookham, 85 feet; and Furze Platt, near Maidenhead, 75 feet. From each of these localities more than 100 implements have been obtained, besides flakes and broken specimens. Flakes were very abundant at Caversham and at Furze Platt, while at Grovelands many bones and teeth of mammoth, horse, and deer were found. Although there is considerable difference in the types of the implements from the various localities in the district, there is little evidence to show whether there was any progress or otherwise in their manufacture during the time their makers lived here. Those from Caversham at the highest level, and presumably the earliest, are more symmetrical in shape and have finer chipping on them than those from Furze Platt, 40 feet lower down, which often appear to have had only a few well-directed strokes given them to bring them to the desired shape. Taking the district as a whole, palæolithic implements occur together in groups in the older gravels, much in the same way as the neolithic ones do in the newer deposits. Caversham and Furze Platt may well have been paleolithic working sites. 1 See Proc. Geol. Assoc vol vii. p. 138, and vol. viii. p. 153. |