STRATIGRAPHICAL GEOLOGY. 527 



into the Eocene, Miocene, and Pliocene formations (ante, 



P- 430 



The systematic limit between the basement beds of the 

 Eocene and the highest horizons of the Cretaceous system had 

 been clearly defined for Northern Europe by Brongniart and 

 D'Omalius d'Halloy, while Buckland had defined the limit 

 between the upper horizons of the Pliocene and the lowest 

 Diluvial or Pleistocene deposits. On the other hand, the 

 difficulty of determining a definite limit between Eocene and 

 Cretaceous deposits in Alpine areas has, except in a few 

 localities, proved insuperable to the present day. 



The characteristic South European and Alpine facies of the 

 Eocene deposits is a massive Foraminiferal limestone, com- 

 posed chiefly of the remains of Nummulites (ante^ p. 244). 

 But in the Alps, this eminently pelagic facies is often partially 

 or wholly replaced by a very variable group of sandstones, 

 marls, conglomerates, shales, and clays, which is termed 

 " Flysch," and offers pakeontological difficulties on account of 

 the rare occurrence of distinctive fossil types, and of many 

 stratigraphical difficulties bound up with the most obscure 

 problems in the tectonic structure of the Alps. 



In 1823, Brongniart had ascertained the Tertiary age of the 

 Nummulite formations at Ronca, Castel-Gomberto, Monte 

 Bolca, and other localities in the Vicentine Alps; and Miinster 

 had published a list of ,one hundred and seventy-two species 

 from the famous locality of Kressenberg in the Bavarian Alps, 

 forty-two of which agreed with typical Tertiary species of 

 Germany, France, and England, while two species showed a 

 certain resemblance to Cretaceous species, and only a single 

 species (Ostrea semiplana) was actually a Cretaceous form. 

 Count Miinster therefore concluded that the Kressenberg 

 strata were of Tertiary age. Murchison and Sedgwick in their 

 memoir on the eastern Alps (1830) also regarded the Kressen- 

 berg strata as Tertiary, but expressed the opinion that the 

 Nummulite rocks near Sonthofen in Bavaria were closely 

 united with the Cretaceous series, as that fauna appeared to 

 contain a fair admixture of Cretaceous and Tertiary types. 



The same opinion was more forcibly expressed by Dufrenoy 

 and Elie de Beaumont in several memoirs explanatory of the 

 geological map of France (1830-38) ; these authors insisted that 

 the fauna of the Nummulite and Flysch deposits in the south 

 of France was a mixed Eocene-Cretaceous fauna closely 



