(1) "On the Geological Relations and Internal Structure of the Magnesian Limestone and the Lower Portions of the New Red Sandstone Series, &c."--'Trans. Geol. Soc.,' ser. 2, vol. iii. Sedgwick. (2) 'The Geology of Russia in Europe.' Murchison, De Verneuil, and Von Keyserling. (3) 'Siluria,' Murchison. (4) 'Permische System in Sachsen.' Geinitz and Gutbier. (5) 'Die Versteinerungen des Deutschen Zechsteingebirges,' Geinitz. (6) 'Die Animalischen Ueberreste der Dyas.' Geinitz. (7) 'Monograph of the Permian Fossils of England' (Palæontographical Society). King. (8) 'Monograph of the Permian Brachiopoda of Britain' (Palæontographical Society). Davidson. (9) "On the Permian Rocks of the North-West of England and their Extension into Scotland"--'Quart. Journ. Geol. Soc.,' vol. xx. Murchison and Harkness. (10) 'Catalogue of the Fossils of the Permian System of the Counties of Northumberland and Durham.' Howse. (11) 'Petrefacta Germaniæ.' Goldfuss. (12) 'Beiträge zur Petrefaktenkunde.' Munster. (13) 'Ein Beitrag zur Palæontologie des Deutschen Zechsteingebirges.' Von Schauroth. (14) 'Saurier aus dem Kupfer-schiefer der Zechstein-formation.' Von Meyer. (15) 'Manual of Palæontology.' Owen. (16) 'Recherches sur les Poissons Fossiles.' Agassiz. (17) 'Ichnology of Annandale.' Sir William Jardine. (18) 'Die Fossile Flora der Permischen Formation.' Goeppert. (19) 'Genera et Species Plantarum Fossilium.' Unger. (20) "On the Red Rocks of England of older Date than the Trias" --'Quart. Journ. Geol. Soc.,' vol. xxvii. Ramsay. CHAPTER XV. THE TRIASSIC PERIOD. We come now to the consideration of the great _Mesozoic_, or Secondary series of formations, consisting, in ascending order, of the Triassic, Jurassic, and Cretaceous systems. The Triassic group forms the base of the Mesozoic series, and corresponds with the higher portion of the New Red Sandstone of the older geologists. Like the Permian rocks, and as implied by its name, the _Trias_ admits of a subdivision into three groups--a Lower, Middle, and Upper Trias. Of these sub-divisions the middle one is wanting in Britain; and all have received German names, being more largely and typically developed in Germany than in any other country. Thus, the Lower Trias is known as the _Bunter Sandstein_; the Middle Trias is called the _Muschelkalk_; and the Upper Trias is known as the _Keuper_.