Ixxxii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



tertiary shells which have been transported into new positions in the 

 diluvial deposits, in order to obtain a perfect view of the molluscous 

 fauna of the tertiary seas of the North of Germany." 



It is well known that Prof. Beyrich and others have looked upon 

 these German Tertiaries as Lower Miocene rather than Upper Eocene. 

 He has founded this opinion on the fact that the oldest Tertiary 

 formation in this part of Germany, which he calls the Magdeburg 

 Sands, agrees most with that of Lethen in Belgium, which belongs 

 to the lower portion of the SystemeTongrien, and immediately overlies 

 the Systeme Lackenien, the uppermost of Dumont's five systems, 

 which, taken together, are the equivalents of the Paris Eocene for- 

 mations up to the sand of Beauchamp, and of those of England up to 

 the Barton clay. In the last part of his work now under considera- 

 tion. Prof. Beyrich explains the reasons which have induced him to 

 adopt a new term to denote this particular formation instead of that 

 of Lower Miocene which he has hitherto used. 



He observes, " Since I determined in the introduction of this 

 work, contrary to the views of Lyell, to call the North German equi- 

 valents of Dumont's Tongrian and Rupelian system Lower Miocene 

 rather than Upper Eocene, the contents of the separate faunas, which 

 all belong to the same system, have been greatly increased by the 

 communications which I have received from all directions. The in- 

 dependent separation of these faunas, both from the Eocene below, as 

 well as from the Miocene above, with which they are only connected 

 at their respective limits by a greater number of common species, has 

 been thoroughly established at every successive step of the inquiry. 

 I have, therefore, thought it desirable to recognize this peculiar 

 Tertiary group as a separate independent formation, by giving it a 

 new and specific name. For this purpose I proposed, in a former 

 Memoir on the position of the Hessian Tertiary formations, the name 

 of Oligocene, a word in evident etymological connexion with the 

 universally adopted terminology of Lyell, and also expressing an idea 

 between Eocene and Miocene." 



This proposal of Prof. Beyrich is, perhaps, under the circumstances, 

 the best that could be adopted. It is an additional yjroof of what has 

 been already advanced in these rooms respecting the impossibility of 

 fixing precise limits between different formations, and of the probabi- 

 lity that as our knowledge increases we shall be compelled by degrees 

 to abandon all those breaks and subdivisions which were formerly 

 looked upon as the legitimate boundaries between successive geolo- 

 gical periods. It is a term which may be appropriately applied to the 

 formation of the Mayence basin, for which I have also advocated the 

 term of Lower Miocene instead of Upper Eocene, inasmuch as it re- 

 cognizes that formation as marking the commencement of a new series 

 of deposits, in accordance with the facts themselves, rather than the 

 conclusion of an old series ; and at the same time it meets the views 

 of those who were unwilling to recognize a Miocene fades in the 

 fossils of that region. 



In the course of last summer I communicated to the Society a short 

 notice from Prof. Beyrich, in which he observed, with reference to my 



