In 1847 the oldest known reptiles were found in the coal field of Saarbrück, in the centre of spheroidal concretions of clay iron-stone, which not only faithfully preserved the skulls, teeth, and the greater portions of the skeletons of these ancient lizards, but even a large part of their skin, consisting of long, narrow, wedge-shaped, tile-like, and horny scales, arranged in rows. What a lesson for human pride! The pyramid of the Pharaoh Cheops, reared by the labour of thousands of slaves, has been unable to preserve his remains from spoliation even for the short space of a few thousand years, and here a vile reptile has been safely imbedded in a sarcophagus of iron ore during the vast period of many geological formations. Still more recently (1854) other wonders have been brought to light in the clay iron-stone of Saarbrück. The wing of a grasshopper, with all its nerves as distinctly marked as if the creature had been hopping about but yesterday, some white ants or termites (now confined to the warmer regions of the globe), a beetle, and several cockroaches, give us some idea of the insects that lived at the time when our coal-beds were forming. Another highly interesting circumstance, relating to the fossils of that distant period, is that in several of them the patterns of their colouring have been preserved. Thus _Terebratula hastata_ often retains the marks of the original coloured stripes which ornamented the living shell. In _Aviculopecten sublobatus_ dark stripes alternate with a light ground, and wavy blotches are displayed in _Pleurotomaria carinata_. From these facts Professor Forbes inferred that the depth of the seas in which the Mountain Limestone was formed did not exceed fifty fathoms, as in the existing seas the Testacea, which have shells and well-defined patterns, rarely inhabit a greater depth. The Magnesian Limestone or Permian group is remarkable chiefly for the vast number of fishes that have been found in some of its members, such as the marl slate of Durham and the Kupferschiefer, or copper slate, of Thuringia. From the curved form of their impressions, as if they had been spasmodically contracted, the fossil fish of the latter locality are supposed to have perished by a sudden death before they sank down into the mud in which they were entombed. Probably the copper which impregnates the stratum in which they occur is connected with this phenomenon. Mighty volcanic eruptions corrupted the water with poisonous metallic salts, and destroyed in a short time whole legions of its finny inhabitants. [Illustration: VENTRICULITES—FOSSIL SPONGE (CHALK).]