The recent discoveries of a living saurian in New Zealand so closely allied to this supposed extinct division of the Lacertilia seems to afford an illustration of a principle pointed out by Mr. Darwin of the survival in insulated tracts, after many changes in physical geography, of orders of which the congeners have become extinct on continents where they have been exposed to the severer competition of a larger progressive fauna. Fig. 392: Tooth of Labyrinthodon. Teeth of Labyrinthodon (Fig. 392) found in the Keuper in Warwickshire were examined microscopically by Professor Owen, and compared with other teeth from the German Keuper. He found after careful investigation that neither of them could be referred to true saurians, although they had been named _Mastodonsaurus_ and _Phytosaurus_ by Jäger. It appeared that they were of the _Batrachian_ order, and of gigantic dimensions in comparison with any representatives of that order now living. Both the Continental and English fossil teeth exhibited a most complicated texture, differing from that previously observed in any reptile, whether recent or extinct, but most nearly analogous to the _Ichthyosaurus._ A section of one of these teeth exhibits a series of irregular folds, resembling the labyrinthic windings of the surface of the brain; and from this character Professor Owen has proposed the name Labyrinthodon for the new genus. Fig. 393 of part of one is given from his “Odontography,” plate 64, A. The entire length of this tooth is supposed to have been about three inches and a half, and the breadth at the base one inch and a half. Fig. 393: Transverse section of upper part of tooth of Labyrinthodon Jaegeri. _Rock-salt._—In Cheshire and Lancashire there are red clays containing gypsum and salt of the age of the Trias which are between 1000 and 1500 feet thick. In some places lenticular masses of pure rock-salt nearly 100 feet thick are interpolated between the argillaceous beds. At the base of the formation beneath the rock-salt occur the Lower Sandstones and Marl, called provincially in Cheshire “water-stones,” which are largely quarried for building. They are often ripple-marked, and are impressed with numerous footprints of reptiles. The basement beds of the Keuper rest with a slight unconformability upon an eroded surface of the “Bunter” next to be described. Fig. 394: Single footstep of Cheirotherium.