cretaceous south north france southern rocks
CONTINENTAL E UROPE. --The Cretaceous system in many detached areas covers a large extent of the Continent. Front the south of England it spreads southward across the north of France up to the base of the ancient central plateau of that country. Eastwards it ranges beneath the Tertiary and post-Tertiary deposits of the great plain, appearing on the north side at the southern end of Scandinavia and in Denmark, on the south side in Belgium and Hanover, round the flanks of the Harz, in Bohemia and Poland, eastwards into Russia, where it covers many thousand square miles up to the southern end of the Ural chain. To the south of the central axis in France, it underlies the great basin of the Garonne, flanks the chain of the Pyrenees on both sides, spreads out largely over the eastern side of the Spanish table-land, and reappears on the west side of the crystalline axis of that region along the coast of Portugal. It is seen at intervals along the north and south fronts of the Alps, extending down the valley: of the Phone to the Mediterranean, ranging along the chain of the Apennines into Sicily and the north of Africa, and widening out from the eastern shores of the Adriatic through Greece, and along the northern base of the Balkans to the Black Sea, round the southern shores of which it ranges in its progress into Asia, where it again covers an enormous area.
A series of rocks covering so vast an extent of surface must needs present many difkrenees of type, alike in their Ethological characters and in their organic contents. They bring before us the records of a time when one continuous sea stretched over all the centre with most of the south of Europe, covered the north of Mika, and swept eastwards to the far east of Asia. There were doubtless many islands and ridges in this wide expanse of water, whereby its areas of deposit and biological provinces must have been more ur less sharply defined. Sonic of these harriers can still be traced, as will be immediately pointed out.
The accompanying table contains the subdivisions of the Cretaceous system which have been adopted in a few of the more important areas of Continental Europe.
It will be seen from this table that while there is sufficient palicontological similarity to allow a general parallelism to be drawn among the Cretaceous rocks of western Europe, there are yet strongly marked differences pointing to very distinct conditions of life, and probably, in many cases, to disconnected areas of deposit. Nowhere can these contrasts be more strikingly seen than in crossing from the Cretaceous basin of the Loire to that of the Garonne. In the north of France the Upper Cretaceous beds are precisely like those of England, the soft white Chalk forming a conspicuous feature in both countries ; but, on the south side of the great axis of crystalline rocks, the soft chalk is replaced by hard limestones. There is a prevalence of calcareous matter, often sparry, throughout the whole series of formations, with comparatively few sandy or clayey beds. This mass of limestone attains its greatest development in the southern part of the deparlment of the Dordogne, where it is said to be about 800 feet thick. lint the Ethological differences are not greater than those of the fossils. In the north of Trance, Belgium, and England, the singular molluscan fancily of the Hippuritida or Budistes appears only oceasionaEs and sporadically in the Cretaceous rocks, as if a stray ibtlividual had from time to time found its way into the region, but without being able to establish a colony there. In the south of France, however, the hippurites occur in prodigious quantity. They often mainly compose the limestones, hence called hippurite limestones (Iludisten-Ka/ke). They attained a great size, and seem to have grown on immense banks like our modern oyster. They appear m successive species on the different stages of the Cretaceous system, and can be used for marking pahvontologieal horizons, as the cephalopods are elsewhere. But while these lamellibranehs played so important a part throughout the Cretaceous period in the south of France, the numerous ammonites and belemnites, so characteristic of the Chalk in England, were absent from that region. This very distinctive type of hippurite limestone has so ranch wider an extension than the English type of the Cretaceous system that it should be regarded as really the normal development. It ranges through the Alps into Dalmatia, and round the great Mediterranean basin far into Asia. Giimbel has proposed to group the European Cretaceous rocks into three great regions : - (1) the northern province, or area of white chalk with Belemnitella, comprising England, northern France, Belgium, Denmark, Westphalia ; (2) the Hereynian province, or area of Esogyra eolumba, embracing Bohemia, Moravia, Saxony, Silesia, and central Bavaria ; and (3) the southern province, or area of hippurites, including the regions south of the crystalline axis of France, the Alps, and southern Europe.
The Wertlden beds, with the Hastings Sands and Weald Clay, are found in north-west Germany. They contain abundant remains of terrestrial vegetation, which is sometimes aggregated into thin seams of black glancing coal, occasionally even as much as 61 feet thick. The marine or typical Neocomian series attains a great development among the eastern Alps, where it consists mainly of massive white and grey limestones, divided into zones according to their characteristic fossils. Some geologists place in it a part of the massive Vienna sandstone (Wiener Sandstein) which enters so largely into the structure of the outer Alps. The massive arenaceous formation formerly massed together under the general name of Quader-sandstein, but now found to be the equivalent of the calcareous bands of other regions, and capable of subdivision into the chief normal groups, forms a conspicuous feature in Saxony and Bohemia, as in the great gorge of the Elbe and the picturesque crags and pinnacles of Saxon Switzerland. From the Upper Cretaceous beds, in the neighbourhood of Aix-la-Chapelle, consisting of white sands and laminated clays 400 feet thick, a large number of terrestrial plants have been obtained. The number of species is estimated at more than 400. Of these 70 or 80 are eryptogams, chiefly ferns (Gleichenia, Lygodium, Aeplcnium, &e.); there are numerous conifers (some akin to Sequoia), and three or four kinds of screw-pine (Pa9tclanus). This flora has a much more modern aspect than any other yet found in Secondary formations. But its most important feature is the occurrence of numerous true exogenous plants - the earliest yet found in Europe. The prevalent forms are Prolcacece, many of them being referred to genera still living in Australia or at the Cape of Good Hope. There occur also species of oak, bog-myrtle, Sze. These interesting fragments serve to indicate the modern character of the flora of Europe towards the close of the Cretaceous period, and to show that the climate, doubtless greatly warmer than that which now prevails, nourished a vegetation like that of some parts of Australia or the Cape. Further information has been afforded regarding the extension of this flora by the discovery in North Greenland of a remarkable series of fossil plants. From certain Lower Cretaceous beds of that Arctic region, Heer has described 30 species of ferns, 9 cycads, and 17 conifers ; while, from the Upper Cretaceous rocks of Nonrsoak, he enumerates species of poplar, fig, sassafras, credneria, and magnolia.