Whether therefore we investigate the physical position of the older glacial shell-beds of Scotland and Norway, their order and elevation, or their fossil contents, we find that they unfold a series of parallel phenomena, and suggest problems which refer to cosmical causes rather than the accidents of local circumstance. II. The second great series of beds indicates a change from the extreme arctic conditions of the preceding period. 1. There are sufficient proofs, we believe, that the change of climate did not take place suddenly. The phrase "Raised Beaches" entirely fails to express the varying characteristics of the beds usually compre hended by it. It is necessary to study each deposit by itself, and carefully catalogue the contents, with the proportions in which the species occur; and different zones of marine life will frequently be found comprised under the general term "Raised Beaches." Many of the Norwegian beds contain a mingling of arctic species with a large development of those, now the common inhabitants of the neighbouring seas. The first characteristic indeed of these semi-glacial or postglacial beds, is the very large increase in the number of species contained. Individual specimens may be as abundant in some glacial as in some later deposits, but invariably, species are far fewer in the more arctic clays. We previously quoted the fact, that Sars has collected fifty-nine species of mollusca from the glacial beds; from the succeeding series, he has catalogued 175. In these deposits also, both individual specimens of arctic species, as well as arctic species themselves, are less predominant. We have reached the period at which arctic forms have not left the waters, but have received a check, and are being driven northward to a more congenial clime. Magnificent examples of this class of beds occur near the small town of Skien, on the northern side of the Christiania fjord. At the south end of the beautiful lake Nordsaeen is a large shell bank, scattered in massive undulations over many acres. Its elevation is about 100 feet above the sea. It contains 128 species of mollusca, a number in itself far exceeding that contained in the whole of the older glacial clays. Among these 128 species, there are very few that may not be found living in Christiania fjord; but these few are arctic in character. For example, Pecten islandicus is small and rare; Tellina calcarea is large and tolerably abundant; but some characteristic arctic species have disappeared. Leda arctica, and even Astarte borealis are absent; while the relative proportion of the remaining glacial forms has become entirely subordinate. The same phenomenon is developed in a large series of similar beds, spread over the west of Norway; and appears conclusively to establish the gradual character of the climatic change. In Scotland, careful study of the clay-pits will, we think, manifest a corresponding fact. On the lower part of the Dalmuir deposit, e. g., is a sandy clay, in which the arctic mollusca are very large and abundant; but in the upper part of the bank, they are neither so large nor plentiful. The general aspect of a collection made from the upper and compared with one from the lower part, of almost any clay bed in the nighbourhood of Paisley, will indicate a striking difference of condition. At the base, resting either on the boulder clay or the native rock, is the laminated mud, with a few foraminifera, evidently indicating conditions unfavourable to molluscan life. This is followed by a large and fine development of arctic shells, which often are so plentiful as to interfere with the economic working of the clay. These shells, however, gradually become more and more rare. Evidently they have been driven away by the shallowing of the water and other physical alterations. At last, in the uppermost marine clay, scarcely a shell occurs, until in the sands and gravels of the old river bed we have the remains of a fresh-water fauna. These deposits thus unfold a series of changes from the comparatively deep waters of the glacial sea, to the estuary of the ancient Clyde; and their evidence corresponds with that of the Norwegian beds, in emphasizing the quiet and gradual nature of the successive steps. The elevation of the land, which took place during this period, has left its record in the existence of fossil beds, both of deep sea and of littoral character. In the island of Barholmen, off Dröbak, a remarkable instance occurs. A fossil bank, reaching from the sea level to the height of 20 or 30 feet, contains a wonderful and peculiar deep-sea fauna. Oculina prolifera is abundant, a coral which, Sars states, is found on the north and west coast of Norway, but never at a less depth than from 150 to 300 fathoms. A clear proof of the elevation of the land to the extent of, at least, 800 feet, is thus obtained. The argument is strengthened by the association with Oculina prolifera of both mollusca, entomostraca, and foraminifera, characteristic of great depths of water. Lima excavata is found, abundant, and of very large size, together with Pecten vitreus and Pecten aratus. At the summit of this island, a height of about 100 feet, a fossil bank also appears. This contains fragments of Oculina and a few of the shells common in the shore bed, but they are associated with littoral species. Littorina littorea, e.g., is most abundant, and completely characteristic of the deposit. The upper and the lower banks on Barholmen thus belong to the same age, but the one is littoral in its character, and the other must have been uplifted from beneath a very great depth of water. In these beds at Barholmen, the peculiar species of the older arctic clays do not occur, and they must be classified in the postglacial series. An elevation of at least 800 feet therefore has taken place in this district, since the retreat of the arctic mollusca to their present latitude. There are also signs in Scotland, of elevation of the land since the glacial epoch. The large bed of Ostrea edulis, which extends through the whole plain at Stirling, and is associated with a clay containing several specimens of the whale, is post-glacial, and the shells are undoubtedly in situ. In the course of the river Irvine, the following section occurs:-(1) clay, with Cyprina islandica; (2) sand, with remains of whale; (3) purely littoral sand both in aspect and contents, equivalent to that on the present shore. The gradual upheaval of the land in post-glacial times, converting the habitat of Cyprina islandica over which the whale journeyed into the shallow sandy shore which became its tomb, is by this section very closely indicated. The courses of arctic currents and of currents equivalent to the Gulf-stream, must have been greatly affected by the physical alterations in the relative position of land and water, produced during the history now briefly sketched, and have acted upon the direction of the isothermal lines. In certain beds, the fauna appear to indicate results of this description. At Bisæt, near Christiania, Isocardia cor, a shell which inhabits the Mediterranean, as well as the southern parts of the Scandinavian waters, is associated with the eminently arctic species Tellina calcarea. A corresponding fact may perhaps be quoted from the Hebrides at the present day, where several especially northern forms reach their most southern limit; and certain peculiar species have no locality recorded between that district and the Mediterranean. A fossil bed at half-tide mark, in the Kyles of Bute and other localities, differs somewhat in its contents from the present fauna of the district. Pecten maximus and Ostrea edulis are far larger than now found in the Firth, while Psammobia Ferroensis and Tellina incarnata are more abundant than in recent dredgings in the neighbourhood. Reviewing the various points indicated in the present paper, we arrive at the following suggestions for further investigation: (1) The course of physical changes from the glacial epoch to the present day, was the same in its broad outlines in Norway and Scotland. (2) These changes were gradual and have left their evidence in the shell-beds as well as in physical phenomena. (3) It is necessary, therefore, to separate and classify these various shell-beds and not include them under the general names of "Drift" and "Raised Beach. " * See Reports by Mr. Gwyn Jeffreys on Dredging among the Hebrides. (4) A general order of succession and variation in the glacial deposits characteristically prevails both in Scottish and Norwegian localities, and embraces the phenomena of an epoch, rather than the merely subordinate accidents of local circumstance. III. ON THE IRON-PYRITES MINES OF ANDALUCIA. By A. H. GREEN, M.A., F.G.S., of the Geological Survey of England and Wales. FOR abundance and variety of 'mineral products, scarce any land in the world can match Spain; but owing to the state of torpor into which this once active country has fallen, it has become all but a matter of impossibility to work her mines with profit. English and French capital and energy have, however, of late, in many instances, successfully battled with the difficulties of such an undertaking; and among the districts thus opened out is a mineral tract reaching across the western part of Andalucia and the adjoining portion of Portugal, which contains many very large and remarkable deposits of Iron-pyrites. My own knowledge of this ground was gathered during rather a hasty visit, but I have been able to add to it from the works quoted below: these, however, are but little known to general readers, and are besides of a somewhat technical character, and I therefore hope that the rather more popular account which I am undertaking may be neither unacceptable nor superfluous. The rock of the district is clay slate, Silurian in age,t bedded, but not cleaved; talcose and micaceous slates are also met with, and here and there beds of quartzite. The strata rear up at very high angles, and are much contorted; but I was told that a general northeasterly and south-westerly strike could be traced. Över the slate tract are scattered many "masses of porphyry of different kinds, passing here and there into diorites, accompanied at some points by masses of cupriferous iron-pyrites, which at the surface are represented by deposits of oxide of iron, known in the country by the names of colorados, monteras de hierro, or requemones. The porphyritic masses are as a rule not very large, of small breadth, and *Notes on the Copper Mining Districts of the Provinces of Seville and Huelva.' By James Mason. London. 1858. 'Notes on the Mines of Rio Tinto.' By J. Lee Thomas. London. 1865. 'Memoria sobre las Minas de Rio Tinto:' presentada al Gobierno de S. M. Madrid. 1856. Carte Géologique de l'Espagne et du Portugal.' M. E. de Verneuil et E. Collomb. Paris. 1864. |