The author thinks it desirable that some of the more definite forms among the variety found on the slabs from the footprint bed' at this quarry should be accurately determined, if possible, instead of being included, as at present, under the general term of 'Cheirotherian.' The author pointed out that, although fifty years have elapsed since its original discovery, the nature of the animal which made the impressions is still as much a mystery as ever; and that the more we study the known forms of Labyrinthodonts, we are forced to conclude that, whatever was the animal by which the larger five-toed footprints at Storeton were made, it cannot be referred to any known species of Labyrinthodont. Dr. Tempest Anderson exhibited in the Geographical Section Room a series of lantern slides illustrating the volcanoes of Iceland. MONDAY, AUGUST 13. The following Reports and Papers were read: 1. Report on Erratic Blocks. [Will be published in the Report for 1895.] 2. Report of the Committee on the High-level Shell-bearing Deposits of Clava, &c.-See Reports, p. 307. 3. On some Lacustrine Deposits of the Glacial Period in Middlesex. By HENRY HICKS, M.D., F.R.S., F.G.S. In this paper the author refers to some deposits, consisting of stratified gravels, sands, and clay, varying in thickness from a few feet to over 20 feet, which are spread out over the plateaux of Hendon, Finchley, and Whetstone. They are frequently covered over by the chalky Boulder Clay with northern erratics; but seldom themselves contain other materials than those which could have been derived from the Tertiary or Cretaceous series in the south-east of England. No marine fossils of contemporaneous age have been found in these deposits, but remains of land animals occur occasionally in and under them. The author has found that their geographical distribution is much wider than has usually been supposed, and he has been led to the conclusion that they must have been deposited during the glacial period in a lake, whose waters attained to a height of nearly 400 feet above present O.D. This lake, he believes, occupied a considerable area in the south-east of England, and spread for some distance south of the Thames, but was dammed up on the east and west by ice and morainic matter. As the lake became gradually reduced in size, lakelets were formed in the Thames valley, and the stratified deposits now found there, except those in the immediate proximity of the present Thames and its tributaries, date back to that period. Man, however, lived in the valley before any of these deposits were thrown down; hence it is that the flint implements and the mammalian remains usually occur under, or in the lower parts of, the deposits. 4. On Sporadic Glaciation in the Harlech Mountains. The author drew a distinction between two results of glaciation-the one, negative, in which the rocks are rounded and striated, and all or nearly all the débris removed; the other, positive, in which the rocks are covered by a thick deposit of drift with boulders. In the Harlech Mountains district areas showing these opposite results lie side by side. Most of the glaciation is of the negative kind, but the areas drained by the Crawcwellt and the Ysgethin are covered by glacial cones of dejection. This difference is accounted for in the first instance by the local drainage being opposite to the general drainage, and in the second by the small size of the gathering ground for the ice. From these results it was argued: 1. That drift deposits are, as a rule, left beyond the area of ice-flow. 2. That no submergence could possibly have taken place here since the Glacial period, or the features above noted would have been obliterated. 5. On the Probable Temperature of the Glacial Epoch. The Alps afford a means of estimating the highest mean annual temperature at which glaciers can begin to form. This must not be more than about 27° F. They also indicate the limits between which glaciers of various moderate sizes form. The author finds that (assuming the present levels of sea and land unchanged) a fall of 20° F. might just bring the Welsh glaciers down to the sea-level, would certainly do it for the Cambrian hills, and would probably produce an ice-shed in the Highlands. A slightly less fall would suffice for the Alps and Pyrenees. Again, a consideration of the traces of glaciers in the Sierra Nevada, Sierra Guadarama, the Apennines, Corsica, Auvergne, the Vosges, and the Schwartzwald shows that these indicate a fall of about 15°, while a greater lowering of temperature would make their glaciers too large. The requirements of North America, New Zealand, Australia, and Tasmania, and other places would be satisfied by about 15°, and in some cases by less. The limits accordingly of the temperature of the glacial epoch must be from about 12° to 20° lower than at present, according to situation. 6. On the Inadequacy of the Astronomical Theory of Ice Ages 1 and Genial Ages. By EDWARD P. CULVERWELL, M.A., F.T.C.D. In reference to Sir Robert Ball's numbers, 63 and 37, giving the proportion of summer and winter heat in the northern hemisphere, the numbers on which he bases his theory, it is pointed out that in the latitudes with which the Ice Age is concerned the contrast between summer and winter heat is vastly greater than is shown by these numbers, which lump together the heat everywhere, at the equator, the poles, and the intermediate latitudes. Nevertheless, though the arguments on which the theory is based may be made much more clear and striking by taking the heat distribution over the northern part of the hemisphere, the method of calling on the imagination to conceive what vast differences of terrestrial temperature may be produced by a slight change in the daily distribution of the (unchanged) annual heat is dangerous as not being sufficiently based on experience. The argument is that, as the earth is kept at a temperature of, say, 400° F. above zero by sun heat, we might expect a fall of 10 per cent. to lower the temperature by, say, 40° F. But in this argument a number of very important elements are overlooked-the diminished radiation from the cooler body, the great time required for any considerable cooling, and the flow of heat by water and air from the hotter to the cooler parts of the terrestrial surface. In fact, so. greatly do these causes modify the result that in these islands we now live without inconvenience in a state of deprivation of solar heat during our coldest 199 days somewhat greater than that which, continued for the 199 days winter of the great eccentricity period, was believed by Sir Robert to involve necessarily an ice age over the northern hemisphere. The estimation of the change in terrestrial temperature due to the changes of eccentricity made in the author's communication is obtained by an entirely A paper giving details of the calculation will be published in the Phil. Mag. different method. The comparative amounts of solar heat for the various latitudes are calculated (a) for the glacial' winter of 199 days and (b) for the coldest 199 days of our present winter. The result may be expressed thus: In. the glacial' winter latitudes 40°, 50°, 60°, 70°, and 80° receive about as much heat in their 199 coldest days as 44°5, 54°, 64°, 74°, and 85° receive in the 199 coldest days at present. Hence, so far as solar heat is concerned, the utmost effect of the eccentricity would be to shift the winter isothermals by 4° to the south, the summer isothermals being shifted by a far greater amount to the north. Hence the astronomical theory cannot account for a shift of the isothermals by more than 4° S. in winter and an average of more than 10° N. in summer-a result ludicrously inadequate to produce an ice age in Great Britain or Ireland, or in the United States, unless, indeed, as a result of the 'glacial' winter, latitude 50° receives vastly less heat from the equatorial regions by air and ocean currents than latitude 54° at present receives in an equal time; and the general principle that the passage of heat to equalise temperature is greater the greater the difference of temperature between the hot and the cold body would, if applicable here, show that 50° in the glacial period should receive even more heat than 50° now, so that we should not expect as great a shift as 4°, even without taking account of the increased summer temperature. When we examine the genial age by this method the result is still more remarkable. The calculations in the paper show that the summer and winter isothermals would be shifted by about 20 only of latitude north and south respectively. It seems entirely out of the question that any change, direct or indirect, depending on so slight a cause could enable walnut trees to flourish in Greenland. After a further examination of the astronomical theory as put forward by Croll, the paper deals with the relation of existing ice-fields to isothermals, to isobars, and to contour lines; and the belief of the author is that, while no climatic changes due to causes known to be active at present could account for the genial age, a local glacial period might easily follow from changed barometric conditions, combined with a gradual elevation of land in a northern latitude. Hence it would appear that either genial periods and glacial periods are due to a shift of the pole, or else glacial periods are due primarily to elevation of the land, while the genial age was due to greater solar activity and greater terrestrial heat in the earlier geological ages. 7. On the Mechanics of an Ice-sheet. By Rev. J. F. BLAKE, M.A., F.G.S. The author attempted to explain how an ice-sheet can carry boulders up a slope, and leave them at a height of 1,000 feet or more above sea-level. The sides of the channel are, in the first instance, supposed to be parallel, so that the mass of ice may be represented in a diagram by its longitudinal section. Taking for simplicity the shape of the surface moved over to be represented by two straight lines, one corresponding to the slope down from the mountains, the other the slope up from the sea bottom to the final destination of the boulders, and taking the surface of the ice as flat, the ice-sheet is represented by a triangle. This is supposed to settle down in such a way that though the level of the end is higher, the centre of gravity of the whole is lower. This fall of the centre of gravity is the effective cause of the motion of the ice-sheet, the resistance to be overcome being that of the ice to change its shape. If the ice-sheet be supposed divided into strips parallel to the slope from the mountains, these will be like a series of overlapping glaciers, and under the influence of the pressure will swell out at the bottom, and thus push the further end of the whole mass a little way up the counter-slope. Continual additions of snow at the end where the ice-sheet commences, or elsewhere on its surface, will be cumulative in their effects, and thus the further end of the ice-sheet will ultimately ascend as required. Again divide the triangle into strips by lines parallel to the counter-slope. The lower of these strips will be pressed together, and any point on the base will be carried on in the direction of the whole motion at a greater rate than the higher layers, and thus the stones, &c., on the sea bottom will be pushed up to their final resting-place, and anomalies of distribution might thus be accounted for by the previous dispersal of the boulders. It was then shown that differences in shape of the ice-sheet and its spreading out at the further end will make little difference in the argument, and under certain conditions will aid the motion. The author then discussed the question of the glacial erosion of lakelets, and indicated the conditions under which this is possible, particularly referring to the difference between an ice-sheet such as that dealt with in the paper and an ordinary glacier. 8. Report of the Committee on the Elbolton Cave.-See Reports, p. 270. 9. Report of the Committee on the Calf-hole Cave.-See Reports, p. 272. TUESDAY, AUGUST 14. The following Papers and Reports were read :— 1. On the Permian Strata of the North of the Isle of Man. The main features of the geology of the island are identical with those of Cumberland and Westmoreland. The Ordovician strata form the 'massif' in both areas, and constitute the sea-worn floor upon which the Carboniferous rocks rest unconformably. The Red Sandstone series of Peel, 1,368 feet in thickness, occupies but a very limited area, extending from the Creg Malin, along the sea front, in a line of picturesque cliffs, about one and a half mile to the north-east, and extending inland about 1,700 feet. The rocks may be divided into two distinct groups. First, the Peel Sandstone series, or Rot-Rottodt-liegende, which presents a thickness of 913 feet, and the calcareous conglomerates and breccias of the Stack series, 455 feet thick, representing the magnesian limestone of the Permians. These rocks are faulted into the Ordovician slates, and neither their true base nor their upper boundary is visible. The pebbles of Carboniferous Limestone in the conglomerates point to a post-Carboniferous age, and the physical characters of both divisions are identical with those of the Permian rocks of the North of England, and more particularly with those of the Lake District, of the Vale of Eden and Barrow Mouth, described by Sedgwick, Harkness, Binney, Eccles, and Nicholson. It is clear that north-eastern Ireland, the northern part of the Isle of Man, and the area of the Lake District, including the Vale of Eden, were parts of the same Permian marine basin, in which, as it approached southern Lancashire, the waters became more highly charged with mud, the calcareous element being conspicuous in the one, and being replaced in the other by thick accumulations of marl. 2. The Carboniferous Limestone, Triassic Sandstone, and Salt-bearing Marls of the North of the Isle of Man. By Professor BOYD DAWKINS, F.R.S. The Ordovician slates, quartzites, and conglomerates, and the associated volcanic rocks of the massif of the island gradually pass underneath the sand, shingle, and clay of the Boulder Clay series in going northward along the coast towards Kirk Michael, until they disappear altogether from the cliffs and the shore. They stand up conspicuously along the ancient shore line extending from Kirk Michael to Ballaugh, Sulby, and Ramsey, commanding the low, sandy, and marshy region which forms the northern portion of the island, contrasting in its flatness with the lofty rolling Ordovician hills behind, culminating in Sartfell, Snaefell, and North Barule. This contrast is obviously the result of a difference in the physical character of the rocks in the two districts. The problem as to which rocks underlie the glacial strata in the former, which had occupied the author's mind for many years, is now partially solved by the three borings which have been made under his advice by Messrs. Craine in 1891-4 in search of the Coal-Measures of the Whitehaven field, at the Point of Ayre, at Blue Point, and at Lhen Moar. The boring at Lhen Moar revealed the existence of the Carboniferous Limestone at a depth of 167 feet 6 inches below the drift. The next bore-hole, at Blue Point, about 4,050 feet to the north-east of that at Lhen Moar, revealed the presence of more than 60 feet of Red Sandstone buried 171 feet beneath the drift. The Red Sandstone in this section is, in his opinion, identical with the St. Bees sandstone, or lowest member of the Triassic formation in the district of the Lakes. This conclusion is greatly strengthened by the discovery in the third boring at the Point of Ayre, to the east of the lighthouse, of the Triassic marls with salt, at a distance of a little under five miles from Blue Point. The diamond drill was used from a depth of 452 feet to the bottom. The total thickness of the salt-beds amounts to 33 feet 6 inches, and the bore-hole happened also to intersect a brine run 2 feet 6 inches in depth. If this section be compared with that published by Mr. Dickenson of the saliferous marls of Duacrue, near Carrickfergus, it will be found to be practically identical. The same series of salt-bearing marls is also worked at Barrow-in-Furness and at Preesal, near Fleetwood. The salt-beds in each of these cases are variable in thickness, and those in the Isle of Man are thinner than in the other localities. It must, however, be remembered that the Manx boring has not ' been put down to a sufficient depth to test the true thickness of the salt-field. The discovery is of great theoretical importance, because it links on the deposit at Barrow to that of Carrickfergus, and shows that the Irish Sea was an area in which the salt-bearing Triassic marls were deposited. It points towards the truth of Mr. Dickenson's suggestion that the Cheshire salt-field was formerly continuous with that of Ireland. These marls have since been broken up, faulted, and denuded away in many places. It is an open question how far those of the Isle of Man are now continuous under the sea eastwards to Barrow and Fleetwood, and to the north-west in the direction of Carrickfergus. All these rocks are buried under a great thickness of boulder sand, gravel, and clay, amounting at the Point of Ayre to 298 feet. To this also must be added the height of the drift hills close by, formed of the same materials, which would give the total thickness as not less than 450 feet in the extreme north. The rocky floor on which it rests dips rapidly to the north-east towards the deeper part of the Irish Sea. The discovery of this salt-field is likely to add a new industry to the resources of the Isle of Man. 3. Strictures on the Current Method of Geological Classification and Nomenclature, with Proposals for its Revision. By Sir HENRY HOWORTH, F.R.S. 4. On the Pleistocene Gravel at Wolvercote, near Oxford. By A. MONTGOMERIE BELL, M.A. The section is a typical illustration of a somewhat advanced period of Quaternary time, and in its general features resembles the sections at Hoxne and Bedford, originally published by Sir John Evans, while it is very different from the implementiferous beds of an earlier age which are found on the Greensand escarpment of Kent and Surrey. |