242 



LYELL'S ELEMENTS OF GEOLOGY. 



Origin of Red Sandstone and Marl. 



of the tail, which is much longer than the lower lobe (see Fig. 

 242.), whereas, in strata newer than the Magnesian Limestone, 

 the tail-fin is divided into two equal lobes, as in almost all living 

 fishes, the vertebrse not being prolonged into either lobe. 



The remains of at least two saurian animals of new genera, 

 Paleeosaurus and Thecodontosaurus have been lately discovered 

 in the dolomitic conglomerate near Bristol.* They are allied to 

 the Iguana and Monitor, and are the most ancient examples of 

 fossil reptiles yet found in Great Britain. The Zechstein of 

 Germany is also the oldest rock on the continent in which Sau- 

 rian remains have been found. They are referred to a genus 

 called Protorosaurus, also allied to the Monitor. 



The resemblance above alluded to between the 

 fossils of the Lower New Red system and those 

 of the Coal, is not confined to the mollusca, fish, 

 and reptiles, but extends to the Crinoidea, or 

 Stone-lilies. Thus one species, the Cyathocri- 

 nites planus (Fig. 243.) of the Magnesian Lime- 

 stone of Durham, has been identified by Mr. 

 Miller with a fossil of the Mountain limestone of 

 Bristol.f 



Origin of the New Red Sandstone group. — 

 The red sandstone and red marl, which, in point 

 of thickness, form the most considerable part 

 both of the upper and lower New Red formation 

 Cyathocrinites in England and Germany, may have arisen in 

 MagiSian^a^nd great part from the disintegration of various 

 ston?^*" crystalline, or metamorphic schists ; and some- 

 times, as in parts of Saxony and Devonshire, 

 from porphyritic trap rocks containing much oxide of iron. In 

 some districts of the eastern Grampians in Scotland, as in the 

 north of Forfarshire, the sides of mountains composed of gneiss, 

 mica-schist, and clay-slate, are covered with alluvium, derived 

 from the disintegration of those rocks ; and the mass of detritus 

 is stained by oxide of iron, of precisely the same colour as the 

 Old Red sandstone of the adjoining Lowlands. Now this allu- 

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

 to form strata of red sandstone and red marl, similar to those of 

 the " Old Red" or New Red system, or those of the cretaceous 

 era in Spain (see p. 199.), or those of tertiary origin, as at 

 Coudes and Champheix, in Auvergne, all of which are in litho- 

 logical characters quite undistinguishable from one another. The 



* See paper by Messrs. Riley and Stuchbury, Proceedings Geol. Soc. No. 46. 

 t Sedgwick, Geol. Trans., Second Series, vol. iii. p. 120. 



