In addition, this engraving shows us a series of islets, rising out of a tranquil sea. One of these is occupied by a forest, in which a distant view is presented of the general forms of the grand vegetation of the period. * * * * * It is of importance to know the rocks formed by marine deposits during the era of the Carboniferous Limestone, inasmuch as they include coal, though in much smaller quantities than in the succeeding sub-period of the true coal-deposit. They consist essentially of a compact limestone, of a greyish-blue, and even black colour. The blow of the hammer causes them to exhale a somewhat fetid odour, which is owing to decomposed organic matter--the modified substance of the molluscs and zoophytes--of which it is to so great an extent composed, and whose remains are still easily recognised. [Illustration: Fig. 62.--Producta horrida. Half natural size.] In the north of England, and many other parts of the British Islands, the Carboniferous Limestone forms, as we have seen, lofty mountain-masses, to which the term _Mountain Limestone_ is sometimes applied. In Derbyshire the formation constitutes rugged, lofty, and fantastically-shaped mountains, whose summits mingle with the clouds, while its picturesque character appears here, as well as farther north, in the _dales_ or valleys, where rich meadows, through which the mountain streams force their way, seem to be closed abruptly by masses of rock, rising above them like the grey ruins of some ancient tower; while the mountain bases are pierced with caverns, and their sides covered with mosses and ferns, for the growth of which the limestone is particularly favourable. The formation is _metalliferous_, and yields rich veins of lead-ore in Derbyshire, Cumberland, and other counties of Great Britain. The rock is found in Russia, in the north of France, and in Belgium, where it furnishes the common marbles, known as Flanders marble (_Marbre de Flandres_ and _M. de petit granit_). These marbles are also quarried in other localities, such as Regneville (La Manche), either for the manufacture of lime or for ornamental stonework; one of the varieties quarried at Regneville, being black, with large yellow veins, is very pretty. In France, the _Carboniferous Limestone_, with its sandstones and conglomerates, schists and limestones, is largely developed in the Vosges, in the Lyonnais, and in Languedoc, often in contact with syenites and porphyries, and other igneous rocks, by which it has been penetrated and disturbed, and even _metamorphosed_ in many ways, by reason of the various kinds of rocks of which it is composed. In the United States the Carboniferous Limestone formation occupies a somewhat grand position in the rear of the Alleghanies. It is also found forming considerable ranges in our Australian colonies.