A new superorder of Paleozoic eclochochlian eephalopods, Aslrovioidea superordo nov., is designated. A distinctive feature of this superorder is that the soft eameral tissue enters the siphon cavity and secrets calcareous eameral deposits. This resulted in the destruction of the connecting rings that previously constituted, in conjunction with the septal necks, the compound wall of the siphon. In early (Ordovician) representatives of this superorder, the soft eameral tissue passed through the siphon to destroy, either partially or completely, the connecting rings and to progress occasionally along the internal surface of those rings that remained unde-stroyed as far as several chambers (the order Lituilida Starobogalov, 1983).

Inadequate observation of sedimentary structures has been responsible for incorrect interpretation of the order of superposition in deformed beds and this has led, in turn, to gross errors in stratigraphy and structure. Failure to recognize and utilize those structures which indicate direction of current flow has also led to incorrect, or at least incomplete, understanding of basin development.

Cet Atlas de Pétrologie s'adresse en premier lieu à tous les étudiants engagés en cursus de Licence dans les domaines des sciences de la vie et de la Terre. Construit sous forme de fiches en double page et abondamment illustré, cet ouvrage offre une vision synthétique sur un ensemble de minéraux et de roches magmatiques, sédimentaires et métamorphiques, les plus fréquemment rencontrés et dont la reconnaissance fait l'objet de séances de travaux pratiques. li est aussi l'occasion de découvrir les roches extraterrestres avec l'étude des météorites et d'aborder certains domaines de la géologie appliquée avec l'étude de ressources naturelles dans leurs gisements et leurs utilisations. <...>