342 OEIGEST OF RED SANDSTONE [Ch. XXII. 



member of the trias. That it is really triassic may be deduced from the 

 following considerations. In Wiirtemberg there are two " bone-beds," 

 one of great extent, and very rich in the remains of fish and reptiles, 

 which intervenes between the muschelkalk and keuper ; the other, con- 

 taining the Microlestes, less extensive and fossiliferous, which rests on the 

 keuper, or superior member of the trias, and is covered by the sandstone 

 of the lias. The last-mentioned breccia, therefore, occupies nearly the 

 same place as the well-known English " bone-bed" of Axmouth and Aust- 

 cliff near Bristol, which is shown above, p. 336, to include characteristic 

 species of muschelkalk fish, of the genus Saurichthys, Hybodus, and 

 Gyrolepis. In both the Wiirtemberg bone-beds these three genera are 

 also found, and one of the species, Saurichthys Mougeotii, is common to 

 both the lower and upper breccias, as is also a remarkable reptile called 

 Nothosaurus mirabilis. The saurian called Belodon by H. Von Meyer, 

 of the Thecodont family, is another triassic form, associated at Diegerloch 

 with Microlestes. 



Previous to this discovery of Professor Plieninger, the mott ancient 

 of known fossil Mammalia were those of the Stonesfield slate, above de- 

 scribed, p. 310, no representation of this class having as j'et been met with 

 in the Fuller's earth, or inferior Oolite, nor in any member of the Lias. 



Origin of Red Sandstone and Hock-Salt. 



We have seen that, in various parts of the world, red and mottled 

 clays, and sandstones, of several distinct geological epochs, are found 

 associated with salt, gypsum, magnesian limestone, or with one or all of 

 these substances. There is, therefore, in all likelihood, a general cause 

 for such a coincidence. Nevertheless, we must not forget that there are 

 dense masses of red and variegated sandstones and clays, thousands of 

 feet in thickness, and of vast horizontal extent, wholly devoid of saliferous 

 or gypseous matter. There are also deposits of gypsum and of muriate of 

 soda, as in the blue clay formation of Sicily, without any accompanying 

 red sandstone or red clay. 



To account for deposits of red mud and red sand, we have simply to 

 suppose the disintegration of ordinary crystalline or metamorphic schists. 

 Thus, in the Eastern Grampians of Scotland, in the north of Forfarshire, 

 for example, the mountains of gneiss, mica-schist, and clay-slate, are over- 

 spread with alluvium, derived from the disintegration of those rocks ; and 

 the mass of detritus is stained by oxide of iron, of precisely the same color 

 as the Old Red Sandstone of the adjoining Lowlands. Now this alluvium 

 merely requires to be swept down to the sea, or into a lake, to form strata 

 of red sandstone and red marl, precisely like the mass of the " Old Red" 

 or New Red systems of England, or those tertiary deposits of Auvergne 

 (see p. 199), before described, which are in lithological characters quite 

 undistinguishable. The pebbles of gneiss in the Eocene red sandstone of 

 Auvergne point clearly to the rocks from which it has been derived. The 

 red coloring matter may, as in the Grampians, have been furnished by the 



