PRINCIPLES OF PALEONTOLOGIC CORRELATION 677 



that the various beds of the English Jurassic may be recognized 

 by their fossils, the stratigraphy and paleontology of this forma- 

 tion have been a favorite field for investigation. Jurassic strata 

 with abundant marine fossils are widely distributed in England, 

 France, Germany, and Switzerland, in easy reach of universities 

 and museums, so that the student of these faunas has an unusual 

 wealth of material at hand. And in this western European 

 province comparatively uniform conditions prevailed during the 

 greater part of this time, allowing the faunas to become widely 

 distributed. It is doubtful if any other succession of fossil 

 faunas in the world is so well known as that of the Jurassic of 

 this province, or if anywhere else such minute stratigraphic and 

 faunal division has been successfully carried out ; for there is 

 not a single bed in all the great thickness of Jurassic sediments 

 that does not contain somewhere in this province a rich marine 

 fauna. 



Quenstedt devoted his life to a minute subdivision of the 

 Jurassic of Wiirttemberg, establishing a classification that still 

 holds sway in Germany ; but this classification was based on 

 local faunas, whose appearance and disappearance were caused 

 by insignificant local changes in sedimentation, and it could 

 hardly be used away from the place where it originated. In this 

 scheme the greater unconformities, overlaps, and faunal changes 

 received no more attention than the smaller geologic events. It 

 was, then, merely a useful local classification, although of great 

 value as a starting point in comparative study. 



It was reserved for Albert Oppel, 1 a pupil of Quenstedt, to 

 establish a chronological classification, based entirely on paleon- 

 tology, and independent of lithologic development. For the 

 entire Jurassic formation Oppel recognized thirty-three zones, or 

 subdivisions characterized by certain species that occurred only 

 in these horizons. The species chosen were of the greatest 

 horizontal and the least vertical distribution, and were usually 

 ammonites. These zones were thought by Oppel to be univer- 

 sal, for he was able to recognize them in Germany, Switzerland, 



'Die Jura Formation, 1856. 



