injurious, unless sparingly used. It is poor in organic remains. The principal range of hills of this rock in England, extends from Sunderland to Nottingham. They never rise more than 600 feet · above the sea; are round-topped, and overlie the coal at Cullercoats in Northumberland. A whindyke which here traverses the coal, does not enter into the magnesian limestone; wherefore the latter deposit is judged to be of more recent formation. At Hart, near Hartlepool, it was bored to the depth of 52 fathoms, without getting through it. On the east of the coal-field in Derbyshire, it is about 50 fathoms thick. The inclination of its beds is generally trifling, being conformable to that of the upper strata, except where it is placed over coal, whose slope it follows. The stratification of this rock is exceedingly distinct, and the separate layers of stone seldom exceed the thickness of a common brick. Its character as a soil is very indifferent ; and its springs are not abundant.

To the geological era or locality of superposition of the magnesian or old alpine limestone, belong the pyritous schists of many districts of Germany, which contain fossil remains of the saurian or lizard family, called monitors. Throughout the countries of Thuringia and Voigtland adjoining to Hessia, as far as Franconia and Bavaria, beds of marly and bituminous schist extend, which Werner regards as the lowest of the first floetz sandstone. Being besprinkled with grains of argentiferous copper pyrites, the ore is mined in several places for the two metals, although it is very poor, yielding scarcely two per cent. of

GREAT FOSSIL SPECIES OF THE LIZARD TRIBE. 189

copper. Humboldt says that a similar stratum is found in several parts of America. The German miners call it, naturally enough, the dead bed, because it affords no proper veins of copper. Above this cupriferous schist, lie the calcareous strata, known in that country by the name of zechstein, and comprehended by the French under the class of older alpine limestone; they contain shells and zoophytes, of the earlier kinds, such as entrochi, anomiæ, &c. The gypsum, with its subordinate sal gem, rests over these limestone beds, and is surmounted in its turn, by sandstone covered with a second gypseous formation unaccompanied with salt. Over this gypsum, another limestone, of more modern date reposes, analogous to the Jura. In its calcareous beds, are those great caverns, which were found filled at their first discovery, with bones of bears and other carnivora, to be afterwards described.

Thus we perceive that these strata of bituminous schist are among the most ancient of any which contain the exuviæ of organized bodies not testaceous. From among their tabular slabs, the vast multitudes of fossil fish were extracted, which have rendered the cantons of Mansfeldt, Eisleben, Ilmenau, and other places in Thuringia and Voigtland, so celebrated among those who collect and describe petrifactions.

Many of the fish are pyritified, in consequence of which, they are subject to rapid decomposition on exposure to the air; and have thus been destroyed. They belong to species unknown in the living state among ichthyologists.

The first account of the stone-casts of the reptiles found in these strata was published by Spener in the Miscellanea Berolinensia, so far back as 1710. His specimen was found in the mines of Kupfersuhl, 3 leagues from Eisenach, 100 feet beneath the surface. The bones were in some degree metallised, like the most part of the fish of the same strata. The second published impression, likewise announced to be a crocodile, was the subject of a letter from Henry Link to the English geologist, Woodward, in 1718. It is from the same place, and in the same kind of stone as the preceding. The third is engraved in the treatise de Cupro of the famous Emanuel Swedenborg. It came from the mines of Glücksbrunn near Altenstein, where it was found in 1733. The fourth was extracted in 1793 from the mines of Rothenbourg near the Saale in the territory of Halle, 264 feet under ground. It is at present in the Royal Cabinet of Berlin. These four specimens, found in beds of the same nature, present certainly animals also of the same species, as is obvious from the similarity of form and size of all the common parts, and especially of the spine, the tail, and a portion of the limbs. These may therefore be all employed to reconstruct a complete individual, by attaching to the common trunk, the parts insulated in each specimen.

The form of its head, its teeth wholly sharp, and the magnitude of the vertebræ of its tail, are alone sufficient to show that it was an oviparous quadruped; without recurring to its posterior limbs, which still more strongly confirm this decision. The head has some resemblance to that of a crocodile; but its

very short muzzle, makes it more different from a gavial, than from any other species of lizard reptile. Even the head engraved by Spener, indicates of itself the genus of the animal. Had it been a crocodile, it would have had at least 15 teeth on each side in its lower jaw, and 17 or 18 in the upper, which would have extended to beneath the middle of its orbits. It has, however, only 11, which go back no further than under the anterior angle of the orbit. This is the character of one of those numerous species which have been crowded together by Linnæus under the name of Lacerta Monitor. This first feature, once recognised, is confirmed by all the rest.

Spener conjectures that the length of his animal must have approached to three feet; those of Swedenborg and Link had nearly the same size, which agrees with what the monitors of the most ordinary species usually attain; such as the land and river monitors of Egypt, that of Congo described by Dandin, those of the East Indies, &c.

§ II. RED MARL.

2. Red marl, or new red sandstone, called occasionally Red rock or red ground. It stretches with little interruption from the northern bank of the Tees in Durham, to the southern coast of Devonshire, covering a great extent of country. It appears sometimes as a reddish marl or clay, sometimes as a sandstone, and at others as a conglomerate of different rocks, cemented by marl or sand. It is remarkable for containing gypsum beds, and the great rock-salt formation of England. Coal

strata are seen to dip beneath it. The colour varies from a chocolate to a salmon hue. The red marl is noted for its rhombic fissures. No organic remains whatever have yet been observed in any of the rocks belonging to this formation.

The red marl and its associated magnesian limestone, form the lowest of the nearly horizontal strata which occupy the southern and eastern counties of England; the strata on which these repose are unconformably placed with regard to them, and rise from beneath them often at very considerable angles, into lofty mountains, skirted by the red marl, which occupies the extended planes at their base.

The agitation of the waters would thus seem to have washed that pulverulent deposit down from the sides of the elevated rocks of carboniferous limestone, old red sandstone, transition slate and greenstone, strewing it over the hollows.

Near the head of the western branches of the Trent, the great central plain of the red marl unites with that which occupies almost the whole of Cheshire, the southern part of Lancashire, and the northern part of Shropshire; watered by the Dee, the Weaver, and the Mersey. The valleys of these rivers are covered by the red marl formation, and the central valley that of the Weaver, affords throughout its course abundance of saline springs, containing above 25 per cent. of salt. Gypsum is also abundant. At Northwich in this vale, an extensive deposit of rock-salt has been found, consisting of two beds, together about 60 feet thick. These are supposed to be large insu