510 HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



of Thirria and Thurmann for the most part, but had also 

 introduced several new names. Marcou had distinguished 

 twenty-six sub-groups which very nearly correspond with 

 Oppel's zones, but he had named his sub-groups not according 

 to leading fossils, but from the names of the localities where 

 they were well developed. It was not altogether surprising 

 then that Marcou should raise some doubts regarding the 

 nomenclature proposed by Oppel. The letters which he wrote 

 upon this subject are of interest for their clear representation 

 of the state of Jurassic research at the time, and for many new 

 ideas about the distribution of the Jurassic fossils. Marcou 

 referred to the valuable researches by Edward Forbes, 

 elucidating the differences of marine faunas in the present 

 time, the confinement of certain faunas within definite 

 geographical limits, and the occurrence of particular types at 

 definite ocean-depths. Applying Forbes's principles of bio- 

 logical provinces and bathymetrical horizons to the elucidation 

 of the Jurassic faunas, Marcou drew maps showing the probable 

 distribution of land and water in the successive Jurassic eras, 

 and trying to determine the chief biological provinces in the 

 Jurassic Ocean. He distinguished eight Jurassic provinces, 

 and correlated their geographical position with three "homo- 

 zoic" climatic zones which had exerted an influence on the 

 distribution of the organisms. 



The work of Oppel has undoubtedly exerted a marked 

 influence upon subsequent stratigraphical research. Although 

 many geologists could not feel convinced of the universal 

 application of a sequence of palaeontological zones, the exact 

 method pursued by Oppel gave an excellent precedent, and 

 the study of the local developments of Jurassic deposits was 

 renewed with fresh vigour. A student of Oppel's, W. Waagen, 

 endeavoured to identify the same zones in Franconia and 

 Switzerland ; the name " Jurassic System " was generally 

 adopted after the publication of Oppel's work, and numerous 

 memoirs appeared wherein the older groups were subjected to 

 more detailed examination. Buckman thought it possible to 

 sub-divide the English series into even more limited horizons 

 than were represented by Oppel's zones, and sub-divided the 

 latter into " Hemerae," each of which was characterised by a 

 typical Ammonite species. 



The Jurassic deposits of the Alps, the Pyrenees, the Apen- 

 nines, the Carpathians, the Balkan mountains, the Iberian 



