known that the peroxide of iron, as a thin pellicle, only incrusts the grains of sand that form the New Red and other red sandstones ; and microscopic examination of the New Red Marl proves that the grains or flakes of sandy mud composing it are encased in the same manner*. Both Sandstones and Marls, I believe, have been formed in lakes, and their red colour is connected with this circumstance ; for it seems impossible that an oxide of iron could be deposited from solution in an open sea in sufficient quantity to colour sediments red, though common pink mud might be so formed from the mechanical waste of red granite or other rocks. The remains of land-plants in the Keuper series, and the peculiarities of some of the reptiles of the period, tend to confirm the view that the strata were deposited in inland salt lakes. Their footprints prove that they walked over moist surfaces ; and if these surfaces had been simply left by a retiring tide, they would generally have been obliterated by the returning flood, in the manner that we see every day on our own sandy shores. It seems to me that the surfaces on which we now find fossil footprints were probably rather left bare by the summer evaporation of a lake ; these surfaces were baked by the sun, and the footprints hardened, so as to ensure their perpetuation, before the rising waters brought by flooded muddy rivers again submerged the low flat shores and deposited new beds of silt, just as they do at the present day round the Dead Sea and the Salt Lake of Utah.
The Foraminifera of the Keuper Marls, which are numerous, might just as well have lived in a salt lake as in the open sea†; and the same may be said of Estheria minuta. The single fish of our Lower Keuper Sandstone, Dipteronotus cyphus, will fall under the same category. The Microlestes antiquus, which occurs in the bone-beds of Stuttgart, and in the Red Marls of Watchet, in Somersetshire, according to Mr. Boyd Dawkins‡, proves nothing except that there was land in the vicinity.
- Mr. Ward, of the metallurgical laboratory, Jermyn-street, at my request
discharged the colour from fragments of New Red Sandstone and Marl by an acid solution of protochloride of tin. Both became white. Under the microscope the marl appeared as a very fine-grained sandstone composed of perfectly white minute fragments of silica. In both the grains had evidently been simply coated with a thin pellicle of peroxide of iron. In the sandstone the peroxide of iron was l.89 per cent.
† Species of Foraminifera are exceedingly variable in form ; and many of them have a long range in geological time. They are therefore of little value in helping to the determination of stratigraphical horizons. It may be true, for example, that if the Chalk were entirely composed of Foraminifera it might be difficult to distinguish from deposits now forming in the Atlantic ; but if these Atlantic deposits were, like the Chalk, half consolidated, heaved up, and denuded, geologists would not feel at a loss regarding their age. They would miss, in the first place, all the genera of Cephalopoda characteristic of the Chalk, besides numerous peculiar genera and species of Echinodermata, and, perhaps with one exception, all the species of Brachiopoda common in the Chalk. Further, over large areas, they would be apt to find Tertiary strata of various ages intercalated between the Old and New Cretaceous beds, which would at once furnish a clue to men experienced in field geology.
‡ Mr. Dawkins considers that these strata belong to the Rhaetic beds ; but the marine Rhaetic fossils have not been found so low. p 2
