Triassic series was deposited in inland waters, partly fresh or salt as the case may have been, whereas the continental Trias was partly, at any rate, deposited in areas connected with the sea. If, between the deposition of the New Red Sandstone and Marl in England, the area in which they occur was not for a time depressed beneath the sea, we have a sufficient reason for the absence of the Muschelkalk. There are, indeed, symptoms of a gap in time between our Bunter and Keuper strata, accompanied by slight indications of disturbance and unconformity ; and, at all events, there is in places a very marked overlap of the Marl across the Bunter Sandstone series.
In England there is a perfect physical gradation between the New Bed Marl and the Rhaetic beds, shown by interstratifications of red, green, and grey marls which, varying in different localities, pass by degrees into limestones, sandstones, and black shales. It is therefore impossible to determine precisely where the Rhaetic beds commence in this series ; and, indeed, all through the New Bed Marl there is a tendency to a repetition of the same sort of deposits as those with which the ordinarily recognized Rhaetic beds were ushered in. This is evinced by the frequent local recurrence of green and grey marls, and thin beds of light-grey and whitish sandstones, commonly called the Middle Keuper Sandstones, which, however, occur in many horizons in the New Bed Marl.
I have long held, in common with some other geologists, that our New Red Sandstone was probably deposited in an inland lake, and that our New Bed Marl was "certainly formed in a salt lake*. This belief is founded on the existence of the great deposits of rock- salt common in that formation, on the ground that, such lakes being fed by rivers and having no outflow, concentration of salts ensued by evaporation, and saline deposits were at length formed, in this case consisting chiefly of common salt. To me it seems impossible that solid salt can be deposited in quantity in an ordinary ocean, for the salt in solution cannot be sufficiently concentrated there to permit of deposition. And though wide-spreading cakes of salt have been formed by evaporation in such areas as the Runn of Cutch, yet this seems rather to partake of the nature of an accident than to denote a steady, long-continued train of events like those which marked the deposition of salt in our Keuper series.
Gypsum and other salts accompanying the New Bed Marl may also have been formed in like manner ; and I consider that the peroxide of iron which stains both salt and marl may also have been carried into the lakes in solution as carbonate of iron, and afterwards deposited as a peroxide through the oxidizing action of the air and the escape of the carbonic acid which held it in solution. It is well
- As far as I know, first proposed by the late Professor H. D. Rogers in an.
address to the British Association at Glasgow, 1855, p. 5, " On some of the Geological Functions of the Winds, illustrating the Origin of Salt." Only the title was printed ; hut ever since I have adopted and expounded Professor Rogers's views in my lectures. Mr. Moore mentions " the fresh- or brackish- water deposits of the Upper Trias," Quart. Journ. Geol. Soc. vol. xxiii. p. 458.
