18G0.] witiGnT — lias and bone-bed. 377 



Sehafhiiutl, " Schiefergebilde der Wetzsteinformation mit Gervillien," 

 Gcognost. Untersuch. siiclbayrisclien Alpengebirges, 1851. Von 

 Hauer, " Kossener-Schichten," Jahrbuch der k. k. geologiscben 

 Reichsanstalt, 1853, p. 733. Escher, " Oberes St. Cassian," Geolo- 

 gische Bemerkungcn iibcr Yoralberg, 1853. G umbel, " Gervillien - 

 (Kossener-) Schichten in dcr Grunten," Gcognostiscbe Skizze, 1856. 

 Oppel and Suess, " Kossener-Schichten," 185(3, Sitzungsber. Akadem. 

 Wissenschaffc. Wien, vol. xxi. p. 535. Oppel, " Kossener-Schichten," 

 1857, ibid. vol. xxvi. p. 7 ; "Bone-bed," Juraformation (1856), 

 pp. 16 & 290. Winkler, " Die Scbicbten dcr Avieula contorta inner- 

 und atisserhalb dcr Alpcn," 1859. Oppel, "Die Zone der Avieula 

 contorta''' Wiirttemberg naturw. Jahreshefte, 1859, p. 315. Lyell, 

 " Infra-liassic Strata of Austrian Alps," Supplement to the Manual 

 of Geology, 5th edit., 1857. Suess, "Kossener-Schichten," Leber die 

 Braehiopoden, &c, 1854. Jules Martin, " Infra-Lias " (pars), Pa- 

 leontologie stratigraphique de l'Lnfra-Lias du Departement de la Cote- 

 d'Or, Mem. Soc. Geol. France, 2 e serie, vol. vii. 1860. 



The Avieula contorta beds, as proved by the list of synonyms pre- 

 fixed to this section, have for thirty years engaged the attention of 

 geologists, "who, after much discussion as to their true place in the 

 series, are still divided in opinion as to whether they ought to be con- 

 sidered the upper portion of the Keuper or the basement-beds of the 

 Lias. It is now generally admitted that the fades of the fauna of the 

 Avieula contorta beds has more affinities with the Kossener-Schichten 

 of the Tyrol and the Upper St. Cassian beds of Germany than with 

 the true Lias ; and I shall demonstrate that most of the species of 

 Radiata, MoUusca, and Fishes found in the Avieula contorta beds are 

 special to them, and do not pass into the Lias. 



At one time the Upper St. Caspian beds were considered to belong 

 to the Trias, and the Fishes found therein were registered by Agassiz 

 as Triassicj whilst the Conchifera were remarked to have many affi- 

 nities with species found in the Muschelkalk. A better acquaint- 

 ance with the fauna of the St. Cassian and the Kossen beds has 

 proved, however, that most of the li ading species in these formations 

 are found in the Avieula contorta beds, and that in fact they all 

 belong to one zone of life which lies upon the confines of the Keuper 

 and the Lias formations, having a common boundary-line in the 

 sandstones and shales below that remarkable stratum the Bone-bed, 

 which has been found to occupy the same relative position in the 

 Avieula contorta series of England, France, Luxemburg, Germany, the 

 Tyrol, and the Jura. 



In all these countri ttains portions of the same species of 



Fishes, and probably of Reptiles, under similar fragmentary con- 

 ditions, forming a true Bone-breccia. 



Section at Garden Cliff. — The following section of Garden Cliff on 



the Severn, near Westbury, affords the best ezpositi f the Avieula 



contorta beds in I H >u< i tershire ; and as each stratum rises in bo 

 sii.n by the river-bank, it can be examined and measured with greal 

 exactness. This section differs ill many important points from others 

 which have been published by previous observers, as those of De la 



Vol.. M 1. 1'AKT I. 2 1 



