EEMAEKS. 85 



IV. 

 GEOLOGICAL AND FAUNAL RELATIONS. 



Remarks. 



THE point of view in this chapter naturally rests upon the assumed existence 

 of a persistent series of discoidal shells which formed a continuous radical 

 stock for all the Ammonoidea, beginning in the Silurian and having their last 

 representative in Psiloceras of the Planorbis bed. This, as we have said above, 

 was closely allied to Gymnites of the Trias, and enables us to connect all the 

 Ammonitinae of the Jura directly with the more ancient primary radicals of 

 the central trunk of the genealogical tree. The chronological distribution of this 

 trunk of forms must be actually represented by more or less broken lines, until 

 all the gaps now existing between the different systems or periods in the earth's 

 history have been filled by the progress of discovery. 



The surviving genus of the trunk stock, Psiloceras, consists of a series of spe- 

 cies which we have called the Radical Stock of the Arietidse, which became in 

 the Lower Lias the generator of new series of peculiar modifications, spreading 

 out from Psil. caliphyttum or planorbe like the spokes of a fan, each genetic radius 

 being composed of a separate series of modifications or species. We have given 

 this classification above, and shown that the chronological distribution of the 

 species in each series is in accord with their positions in the series ; it now 

 remains to apply the same classification to the solution of the problems of choro- 

 logical distribution. 



There are many more or less complete lists and monographs of local faunas 

 in the province of Central Europe, and extensive collections, which afford a solid 

 basis for comparison. The preliminary work of Prof. Jules Marcou, 1 in synchro- 

 nizing the minuter subdivisions of the Jura in Central Europe, was completed 

 by the more extensive application of the same principles by Oppel, 2 who visited, 

 studied, and synchronized the faunas of the different localities, and identified the 

 same beds in a large part of this province. The illustrated publications of Hauer, 3 

 Neumayr, 4 Wahner, 5 Geyer, 6 and Herbich, 7 have also thrown a strong light upon 

 the peculiarities of the faunas of the eastern part of Europe, particularly the 

 basin of the Northeastern Alps. All of these researches, and many others not 

 mentioned, have made still further advances in the classification of the chrono- 

 logical relations of the minuter subdivisions or beds practicable. 



1 Roches des Jura, pp. 23, 162, 173, et seq. 



2 Die Jura-Format. Eng. Frankr. u. d. siidwestl. Deutschl. Wurtt. Jahresb., XII. -XIV., 1856. 



3 Die Cephal. a. d. Lias d. norddstl. Alpen, Denksch. Akad. d. Wissensch., Wien, XI. 



4 See note 2, page 86. 6 Mojsis. et Neum., Beitr., II. - VI. 



6 Ceph. heirl. Schich, Abh. k. k. geol. Reichsans., XII. 



7 Das Szeklerland, Mitt. Jahrb. d. k. ungar. Anst., V., Pt. II. 



