512 HISTORY OF GEOLOGY AND PALEONTOLOGY. 



the English geologists assigned the Wealden formation, ex- 

 clusive of the Purbeck strata, to the Lower Cretaceous 

 horizon. 



The definition of a limit has proved even more difficult in 

 the regions with Alpine facies, where there is no littoral series 

 of passage-beds from Jurassic to Cretaceous horizons. Marine 

 strata of Upper Jurassic age are frequently covered conform- 

 ably by similar deposits of Lower Cretaceous age, and any 

 line of separation seems at first sight necessarily of an arbi- 

 trary character. Oppel, in a contribution to the Zeitschrift in 

 1865, opened the question of the Jurassic-Cretaceous limit in 

 the Alps. He comprised under the name of " Tithonian 

 Horizon " a number of Alpine and Carpathian deposits (the 

 Diphya limestones of South Tyrol, the Northern Alps and 

 Dauphine, the Aptychus shales, the upper mountain limesto?ie 

 of the Northern Alps, and the Stramberg strata\ together with 

 the lithographic shales of Bavaria and Nusplingen, the Pur- 

 beck and Portland strata of England and the North of France, 

 and on the basis of their peculiar Cephalopod fauna classified 

 the Tithonian series as an independent group of strata between 

 the Kimmeridge and the Neocomian horizons. Regarding the 

 precise systematic position, Oppel seemed to incline rather to 

 the inclusion of the Tithonian group in the Jurassic system. 

 An enumeration of one hundred and seventeen Cephalopod 

 species, most of them from Stramberg, Rogoznik, South 

 Tyrol, and the lithographic shales of Franconia, affords the 

 evidence upon which Oppel erected the Tithonian horizon. 



Long before OppePs paper, Beyrich had in 1844 drawn 

 attention to the relations of the " Klippen limestone " and 

 "Stramberg limestone"; and Stur, Hauer, Hohenegger, and 

 Suess (1858) had identified both these limestone forma- 

 tions as Upper Jurassic, whereas Zeuschner (1844-48) had 

 assigned the " Klippen " limestones of the Carpathians at first 

 to Upper Jurassic, then to Neocomian, and had stated that the 

 fauna was a mixed Jurassic and Cretaceous fauna. 



Benecke showed, in his able work on the Triassic and 

 Jurassic deposits of the Southern Alps (1866), that two faunas 

 are contained in the red Jurassic Ammonite limestone, the 

 younger of which contains Terebutula diphya as the leading 

 fossil, and a number of peculiar Ammonites. The older is 

 characterised by Ammonites acanthiciis and other Upper 

 Jurassic Ammonites. Benecke paralleled both horizons with 



