AITNIVERSAET ADDEESS OP THE PKESIDEXT. IxV 



In conclusion he observes that this " Etage Infraliasien " may 

 be separated into two subdivisions, which he calls the upper and 

 lower. The upper subdivision contains all the equivalents of the 

 Ammonites-planorhis and A.-angulatus zones ; the lower contains 

 the true equivalents of the Avicula-contorta beds. The petrogra- 

 phical characteristics of the former are chiefly sandstones (gres), 

 limestones, and dolomites ; the second also consists of sandstone, 

 but preferably of calcareous marls. He also proposes to subdivide 

 each of these subdivisions into two zones. Those of the Upper 

 Infralias are already well established. The separation of the two 

 zones of the lower division is for the present only founded on the 

 author's observations in Lombardy. He distinguishes them by 

 certain fossils which are abundant in and peculiar to each, and 

 draws up the following Table : — 



r Upper, Hettange f A. Ammonites-angulatus zone. 

 p, Tif I'ns J beds. \ B. Ammonites-planorhis zone. 



I Lower, Avicula- J C. Terehratula-gregaria zone. 

 (^ contorta beds. \ D. JBactrylliiMn striolatum zone. 

 He then briefly describes the palseontological characteristics of 

 the two divisions of the Infralias, which need not here be intro- 

 duced, and gives a list of the distribution of species in the two 

 strata of the Avicula-contorta beds. 



Another work on this subject is by Dr. v. Dittmar, recently 

 published at Munich. The object of this author is to point out the 

 extent and distribution of this Avicula-contorta bed now found to 

 exist in so many parts of Europe, and to describe the different 

 characters under which it is developed, in order to arrive at the 

 solution of the question, whether it belongs to the Trias or the 

 Lias. 



The author first points out its geographical distribution, and 

 quotes the difierent authors by whom it has been described, whe- 

 ther under this denomination, or as the " Bone-bed," the form in 

 which it generally occurs in Wiirtemberg, the north of Germany, 

 and in England, but which is altogether wanting in the Alps and 

 in Sweden, and is only slightly developed in France. He then 

 describes the different palaeontological features of the formation in 

 diiferent countries, showing from its various contents how it 

 was generally a littoral deposit in England, Erance, and Ger- 

 many, formed in shallow seas and near the coast of continents or 

 islands ; whereas in the Alps, the thick massive limestone-beds 

 by which it is almost everywhere characterized, give it a predo- 

 minantly oceanic character. 



"With regard to the stratigraphical phenomena of the Avicula- 

 contorta bed, the author points out various localities, both in 

 Germany and the Eastern provinces of France, where the lower 

 Liassic beds lie imconformably on the Keuper, whereas in other 

 places these two formations are conformable. He then comes to 

 the really important question as to its geological position, and 

 admits that, after repeated researches in different localities, the 

 main result obtained was that the " contorta zone " appeared to be 



VOL. XXI. « 



