porphyry, and abundance of felspar, both in a decomposed state and in perfect crystals. The magnesian limestone, over the lower red sandstone, should here be described in the ascending series; but the description would disconnect the account of the upper and lower red sandstone, which are strictly but one formation. I shall, therefore, defer the description of the magnesian limestone, until that of the red sandstone is gone through. In fact, the magnesian limestone does not always occur in the red sandstone. New Red Sandstone and Marle above magnesian limestone. The beds have generally the prevailing colour which the name implies, but are often marked with irregular veins and spots, of a yellowish or bluish colour, and the sandstone is sometimes yellow or grey, with occasional spots of red. The composition of different strata in this formation is extremely various: in some parts we find an argillaceous marle in different states of induration, and more or less intermixed with calcareous earth. In other parts we meet with regular strata of siliceous sandstone; and sometimes we have a conglomerate sandstone, or a soft sandstone, enclosing rounded pebbles of quartz and Lydian stone, granite and porphyry, as in the rock on which Nottingham and the Castle stand. In the lower part of this division, as well as in that beneath the magnesian limestone, the beds are porphyritic, and contain imperfect crystals of felspar; sometimes they pass into amygdaloid and trap. The fine siliceous sandstones, when closely examined, are often found to contain fragments of the neighbouring rocks: thus the sandstone in the vicinity of Charnwood Forest, as before stated, contains fragments of slate and chlorite slate; and the conglomerate beds on the northern side of that range of hills, are principally composed of fragments of granitic and slate rocks. No formation presents such a great variety of mineral characters as the red marle and sandstone. In England it has frequently been confounded with the red sandstone and conglomerate, that occur under the upper transition limestone, called by English geologists the old red sandstone. But the old red sandstone of foreign geologists, or roth-todte liegende*, the grès ancien of Daubuisson, covers the coal formation, and therefore corresponds with the lowest beds of the English red marle and sandstone. Where the red marle and sandstone formation is fully developed, it may be arranged, as before stated, under three divisions: the lower, which corresponds with the roth-todte liegende, consisting of fragments of different rocks cemented by sand or marle, and of beds of imperfect porphyry; this occurs below magnesian limestone: the middle beds, consisting chiefly of sandstone, called by the French grès rouge and grès des Vosges: and the upper, consisting of marle and variegated sandstone, in which beds of rock-salt and gypsum occur; this corresponds with the grès bigarré and marnes irrisées of the French. In England the three divisions of this formation rarely if ever occur together, accompanied with magnesian limestone; but it should appear, from the situation of these different beds on the Continent, that the place of the magnesian limestone is between the lower and the middle division; for the magnesian limestone or zetchstein, rests on the conglomerate beds of red sandstone. In the third number of the Annales des Mines, 1827, there is a very full account of the different arenaceous strata that separate the coal strata from lias limestone, along the feet of the Vosges mountains on the eastern side of France, by M. L. Elie de Beaumont. This account throws considerable light on a part of geology hitherto obscured by the conflicting * The name Roth-todte liegende, or red dead lyes, was first applied to what the English call the old red sandstone, below the coal formation, because no coal was found under it. opinions of former observers, and assimilates the red sandstone of France and Germany with the different divisions of the same formation in England. The Vosges mountains are composed of granite and transition rocks, and at their feet there are several coal-fields: the coal strata, and also the lower declivities of the granite, are in part covered unconformably by nearly horizontal strata of red sandstone; and this is covered by lias limestone. We have here, on a larger scale, an exact correspondence with the geology of the Charnwood Forest district, where the granite and slate rocks are bordered by coal strata, and are both partly covered by horizontal strata of red marle and sandstone; and this again is covered by lias limestone. The red sandstone of the Vosges is, however, more developed; the lowest part consists of conglomerate and porphyroidal beds: these cover the coal strata; they agree in their mineral characters precisely with the conglomerates in the English red sandstone, particularly those of Devonshire, and are described by M. Beaumont as being the true rothtodte liegende. Above this occurs a considerable thickness of strata of red sandstone, which passes by gradation into the conglomerate; this is the proper grès rouge: it is designated by M. Beaumont grès des Vosges; it approaches in its character nearer to the grès bigarré than to the lower beds. The variegated sandstone, or grès bigarré, covers the grès des Vosges; but there appears to have been a considerable degradation of the surface of the grès des Vosges, and also a disturbance of the beds by subsidence or faults, before it was covered by the grès bigarré or variegated sandstone: nevertheless they are evidently members of the same formation. In the beds of the grès bigarré there are found thin beds and concretions of magnesian limestone; and above this is a more extensive formation of smoke grey limestone called muschel kalk, abounding in organic remains. In this limestone, the beautiful fossil, the lily encrinite, is found. (See the cut.) The muschel kalk occurs also in Germany, but is entirely wanting in England. In its mineral characters it bears a near resemblance to the limestone called lias, but it is separated from the lias of the Vosges by thick beds, corresponding with the English red marle, but called by the French marnes irrisées, from their spotted and variegated colours. The fossils in the muschel kalk bear a nearer relation to those in the lias than to the shells in the magnesian limestone below it; but neither belemnites nor gryphites occur in this limestone in the Vosges. Its chief fossils are the lily encrinite, two species of ammonite, the terebratula subrotunda, and a species of muscle. According to M. E. Beaumont, were it not for the intervention of the muschel kalk, there would be a complete passage of the red sandstone into the red marle, as occurs in England. It deserves attention, that the lily encrinite has just been discovered in limestone brought from Ireland to the Isle of Wight. The drawing I have seen of it leaves no doubt of the fact; but whether the limestone be mountain limestone, as it is called, or the muschel kalk, remains to be determined. Thick beds of red marl, with fibrous gypsum, compose the upper part of the new red formation in the midland counties of England: the red marl is generally spotted, and striped by greenish and yellow marl. The beds of red marl and sandstone of this formation, occupy a considerable part of the midland counties in England, extending from the eastern side of Yorkshire into Devonshire, and on the west, with some interruption, from Cumberland to Gloucestershire. The beds or strata never attain any considerable elevation in England; they cover or enclose rocks of other formations: in Leicestershire and Warwickshire they surround rocks of sienite, granite, porphyry slate, greenstone, and quartz. The granite and greenstone of the Malvern Hills, are covered on the southern side by the same red marl and sandstone. In Devonshire, several rocks of greenstone and amygdaloidal trap are also surrounded by it; and at Rouvray in France, on the road to Dijon, I observed a low range of sienitic and granitic rocks, rising from a similar red marl, which, like the English red marl, was covered by blue lias with gryphites. It was formerly maintained by Mr. Farey, that the sienitic and granite rocks of Charnwood Forest and Malvern, were merely anomalous masses in the red marl; and though this opinion was deemed extravagant, and afterwards abandoned by Mr. Farey himself, I am inclined to believe, that there is a greater connection between these different formations, than has hitherto been admitted. The red marl and sandstone of England, appear to me to have been principally formed by the disintegration of rocks of trap, greenstone, sienite, and granular quartz: the iron in the decomposing trap rocks, has probably given to this formation its red colour. I conceive that the argillaceous marls have also been principally formed from the trap rocks, and the siliceous sandstones from the granular quartz R |