768 HISTORICAL GEOLOGY. 



basis of the species Laopteryx j^riscus of Marsli. It probably had teeth and 

 biconcave vertebrae. 



4. Mammals. — Remains of Jurassic Mammals have been described by 

 Marsh from the Atlantosaurus series, and mostly from Wyoming, where 

 portions of lower jaws of some hundreds of individuals have been found 

 in thin dirt-beds. (The same beds have afforded, besides Dinosauriau bones, 

 remains of Crocodiles, Turtles, small Lizards, and Fishes, besides the Laop- 

 teryx.) The Mammals were like mice and rats in size, the length of the 

 lower jaw varying from half an inch to one and one half inches. Specimens, 

 more or less perfect, of the jaws of species are shown in Figs. 1225-1249, 

 from Marsh. Ctenacodon has a large cutting incisor, as Figs. 1230-1233 

 show, and is referred, along with the genus Allodon, to the same family with 

 the genus Plagiaidax of Owen. The characters of the others are mostly 

 those of Marsupial Insectivores. The number of teeth in some modern 

 Marsupials is 2 to 4 above the normal number 44; but in the Triassic and 

 Jurassic species, where determinable, as tabulated by Osborn, it is beyond the 

 normal number by 4 to 24 teeth ; the earliest Dromatherium is stated to have 

 had 56 teeth ; the Jurassic Stylacodon, 68. 



FOREIGN TRIASSIC AND JURASSIC. 



1. Triassic. 



At the commencement of the Triassic period, Scotland and western 

 England were mostly dry land. Triassic beds show that the only under- 

 water or rock-making region of western England (Wales included) was 

 that of a broad channel, passing westward over Cheshire to the coast of 

 the Irish Sea by Liverpool, and northward of that city. Eastward, the chan- 

 nel opened into the North Sea of the era, or into its great sea-border flats ; 

 and the shore line stretched northward nearly to Newcastle, thence 

 along by eastern Scotland, and southwestward to Torquay on the British 

 Channel. But the seashore flats appear to have been emerged land over 

 southeastern England, the Triassic being absent according to evidence from 

 borings. In Europe, southeast of England, beyond a broad border region of 

 the continent (now under Tertiary or Cretaceous rocks), Triassic beds again 

 appear over both eastern France and the Netherlands ; and the two areas, 

 united (beneath a strip of Tertiary) behind the Carboniferous area of the 

 Belgian border, continue from the Vosges Mountains to Saxony, Bohemia, 

 and the Juras on the borders of Switzerland, and also along the western and 

 eastern Alps into Italy and Austria. Further, they appear again over a 

 large surface in Eussia, west of the Urals, reaching from the Caspian to the 

 coast east of the White Sea, and again farther north, in Spitzbergen, as 

 already stated. And since the interval between the Triassic outcrops of 

 Austria and Russia, and that between the Alpine and the Franco-Prussian 

 areas are largely under later rocks, it is probable that at this period nearly 

 all outside of Scandinavia and the Baltic provinces in Russia was a shallow 



