§ 1. THE TRIAS AND PERMIAN FORMATIONS. 585 



3. Marl slate, in thin layers, containing reptiles and fishes. The 



Keuper schiefer, or Copper schist of Mansfeld. 



4. Marls and variegated sandstones, with sands and clays of variable 



thickness and character. 



Total thickness, 100 yards. 



From this tabular view, the Trias and Permian systems 

 are seen to consist of variegated blue and red marls and 

 sandstones, magnesian limestones, and conglomerates, more 

 or less coloured with peroxide of iron ; the upper group 

 containing beds of salt and gypsum, and the lower, cal- 

 careous rocks, having in their composition a large propor- 

 tion of magnesia. As a whole, the strata are comparatively 

 scanty in organic remains ; but in some localities plants of 

 several genera and species, — ammonites, nautili, belemnites, 

 and other marine shells, — and Plesiosauri and other reptiles 

 are met with ; certain species and genera being peculiar to 

 each system. 



2. Geographical Distribution of the Trias and 

 Permian. — For the sake of conciseness I shall comprise 

 both systems, in the following brief notice of their geogra- 

 phical distribution.* 



From the river Tees (see the map, PL I. p. 462), on the 

 Yorkshire coast, the line of their emergence from beneath the 

 Lias, forms their eastern boundary; and they extend nearly 

 parallel with the western branch of that formation to the 

 Dorsetshire and Devonshire coasts, near Lyme Regis, 

 Sidmouth, and Torbay.-f But the district of which they 

 form the subsoil, is exceedingly variable in breadth, from 

 the great extension of its western limits. This arises from 

 the saliferous being the last of the nearly horizontal con- 



* In the map, Plate I. the Trias and Permian are both included 

 under the term Triassic, and denoted by the same colour and number 



f This account of the course of the Trias is principally derived 

 from the " Geology of England and Wales." 



