102 Chronicles of Science. [Jan., 



mi Idle course, and treat them as a " distinct formation." This last 

 appears the wisest and most practicable course, although it is often 

 objected to because the middle term, say the objectors, is not of the 

 same value as those on each side ; but inasmuch as the whole Geolo- 

 gical series consists of a great many terms, and it is pretty certain 

 that their values vary almost as much as in the case in question, this 

 objection to a rational solution ought not to outweigh the advantages 

 accruing from its adoption. 



The above paragraph may be considered to represent the state of 

 public Geological opinion, respecting the systematic position of certain 

 strata, known as " the Passage-beds of the Lower Lias," the " Zone of 

 Avicula contorta" the " Rhsetic Beds," the " Kossen Beds," the " Ger- 

 villia-beds," the " Infra-lias " (pars), the " Tabingen Beds," &c, and 

 recently called the ''Penarth Beds" by the Geological Survey. 



Lately several important memoirs have been published, in which 

 this question has been discussed at great length ; their titles and 

 authors are as follows : — " Der Jura in Franken, Schwaben, und der 

 Schweiz." By W. Waagen. Munich, 1864. 



" Der Hannoversche Jura." By Karl Von Seebach. Berlin, 1864. 

 <; Die ContortaZone (Zone der Avicula contorta, Portl.), ihre Verbrei- 

 tung, und ihre organischen Einschlusse." By Alphons von Dittmar. 

 Munich, 1864. 



" Notices Geologiques et Paleontologiques sur les Alpes Vaudoises 

 et les Regions environnantes." By E. Renevier. Lausanne, 1864. 



" Etudes sur les Etages Jurassiques inferieurs de la Normandie." 

 By Eugene Eudes-Deslongchamps. Paris, 1864. F. Savy. 



" On the Rhsetic Beds and White Lias of Western and Central 

 Somerset," &c. By W. Boyd Dawkins. ' Quarterly Journal Geolo- 

 gical Society,' November, 1864 ; and ' Geological Magazine,' December. 

 1864. 



" On the Rhretic or Penarth Beds of the Neighbourhood of Bristol 

 and the South-west of England." By H. W. Bristow. ' Geological 

 Magazine,' November, 1864. Read before the British Association at 

 Bath, 1864. 



The opinions expressed in these several memoirs are as various as 

 they can be, for while Herr Waagen calls the Zone of Avicula contovta 

 the uppermost member of the Keuper, M. Deslongchamps and M. 

 Renevier consider it to belong to the Lias, the former positively, the 

 latter more diffidently ; then again, Herr von Seebach appears unde- 

 cided, Mr. Boyd Dawkins* calls it the Passage-beds of the Lower 

 Lias, and Herr Von Dittmar treats of it as a separate formation ; but 

 the last-named Geologist thinks that if it must be classed with one or 

 the other formation, it should be placed with the Keuper, the balance 

 of authority (!), he considers, favouring that view. The Geological 

 and Pakeontological evidence must indeed be conflicting, when it is 

 found desirable to decide such a question by arbitration, and Herr 

 von Dittmar almost proposes that this should be done. In general 

 terms it may be said that the French and Italian Geologists consider 



* "We shall notice this author's paper at greater length under the head of "Pro- 

 ceedings of the Geological Society," p. 10S.I. 



