STRATIGRAPHICAL GEOLOGY. 509 



In the course of a local study on the Middle Lias in Swabia, 

 he proved himself to be an excellent observer and able pale- 

 ontologist. He then visited the famous " Jurassic " localities 

 in France and England, and endeavoured to compare not only 

 the main sub-divisions, but also the smallest groups of strata in 

 the different areas by means of the fossil species occurring in 

 them. Setting aside all lithological features, Oppel deduced 

 from his observations a series of palaeontological horizons 

 which he termed Zones, each of which represented the definite 

 age-limit of some leading fossil type or types. "A Zone" he 

 says, " is characterised as a definite palceontologica I horizon by the 

 constant occurrence in it of certain species which do not occur in 

 the preceding or succeeding neighbour zones." 



Oppel accepted Buch's division of the Jurassic system in 

 three main groups as the foundation of his own detailed sub- 

 division. He retained the English term Lias for the lowest 

 division, proposed the name Dogger for the middle division, 

 and Malm for the upper division. These names had already 

 been used in England for rocks of different age ; and D'Omalius 

 Halloy had applied Malm to a division of the Cretaceous 

 formation. The three main groups were sub-divided by Oppel 

 in eight zones, which agree in the essential features with those 

 suggested by D'Orbigny, and for which he retained D'Orbigny's 

 nomenclature. He, however, modified D'Orbigny's zones in 

 so far as to omit the " Corallien " and " Portlandien," on the 

 ground that they were local facies of the " Oxfordien " and 

 ' Kimmeridgien." Oppel's sub-division of the whole Jurassic 

 system embraces thirty-three zones, each of which is charac- 

 terised by a particular fossil type. 



Oppel's admirable work, published in 1856-58, was received 

 very favourably throughout Germany, France, and England, 

 the cordiality of the reception being not a little increased 

 owing to the general regard in which the author was held. 

 In France, D'Archiac took objection to certain points, 

 but Jules Marcou, always ready for a scientific debate, lent 

 ardent support to Oppel, and the controversy soon collapsed. 

 Marcou had previously published a loCal monograph on the 

 Jura near Salins (1848). In it he had accepted the divisions 



compare the Jurassic deposits with one another; in 1858 was attached to 

 the staff of the Paloeontological Museum in Munich, in 1860 was appointed 

 Professor of Palaeontology, and in 1861 Director of the Palaeontological 

 Collection in Munich ; died in 1865 from typhoid fever. 



