ORGANIC REMAINS. 431 



animal ; and that the size of the three species corresponded 

 with that of the three different kinds of footsteps which 

 had already been supposed to belong to three distinct 

 individuals. Finally, the structure of the nasal cavity 

 showed the Labyrinthodon to be an air-breathing reptile, 

 since the posterior outlets were at the back part of the 

 mouth, instead of being directly under the anterior or 

 external nostrils. It must, therefore, have respired air, like 

 the saurians, and, in all probability, may have imprinted 

 on the shore those footsteps which were supposed to have 

 been produced by an animal walking on dry land. 



MAGNESIAS LIMESTONE OR ZECHSTEIN. The inferior 

 members of the new red sandstone formation consist, in the 

 south-west of England, of a conglomerate, formed of pebbles 

 cemented together by a base of dolomite or magnesian 

 limestone, whence it is termed dolomitic conglomerate. The 

 imbedded fragments chiefly consist of the debris of the rocks 

 on which they repose, such as fragments of mountain- 

 limestone, coal, shale, and other underlying deposits. In 

 the north of England these conglomerates and breccias 

 are represented by the magnesian limestone. The mag- 

 nesian limestone is now separated from the Trias into a 

 distinct system, under the name of PERMIAN, from Perm, 

 a Russian government ; where strata of this group are 

 extensively developed, occupying an area twice the size of 

 France, and contain ing a special Fauna. Mr. King classi- 

 fies * the Permian group of the north of England into six 

 stages, which he is of opinion represent the Thuringian 

 strata : 



NORTH OF ENGLAND. THURINGIA. 



1. Crystalline limestone. 1. Stinkstein. 



2. Brecciated limestone. 2. Rauchwacke. 



3. Fossiliferous limestone. 3. Dolomit, Up. Zechstein. 



4. Compact limestone. 4. Zechstein, Low. 



5. Marl slate. 5. Mergel-schiefer. 



6. Inferior sandstones. 6. Rothliegendes. 



The magnesiau-limestone has lately been brought into 

 repute for architectural purposes, buildings constructed 

 of it having been ascertained to be extremely durable. The 



* Pal. Soc. Memoir. 



