OF THE SWISS JURA AXD EXGLAND. 



251 



The Astartian beds in the two districts have many characters in 

 common, and are approximately on the same horizon ; and the same 

 may be said of the Pterocerian, except that the latter is considerably 

 thicker in the southern district. 



It has already been pointed out that the Yirgulian is hardly 

 represented in the southern district, unless it be by the marly bed 

 at the base of the Portlandian. 



The two remaining stages, the Portlandian and Purbeckian, are 

 found principally in our southern district, and those recorded from 

 the one locality, Aloutier, in the northern district are probably on 

 the same horizon as those similarly named in the southern district. 



3. Correlation. 



When the Upper Jurassic rocks of the Jura are compared with 

 those of England, one cannot fail to notice the marked dissimilarity 

 which occurs in their lithological character ; and this is best shown 

 in the upper part of the series, which, in England, consists of the thick 

 clays of Kimeridge and the more variable Portland and Purbecks, 

 whilst in the Jura they are formed of massive limestones. There is, 

 however, a strong resemblance in some of the lower beds in the two 

 areas, and indeed some of them are almost identical in their litho- 

 logical character. The difference in the nature of the rocks is, of 

 course, accompanied by a difference in their fauna ; and on this 

 account it will not, in all cases, be easy to establish the true syn- 

 chronism of the stages in the two countries. Certain well-marked 

 zones are present in both areas, and these are of great service in 

 working out the correlation of the remaining zones. 



Oppel, in his ' Jura-formation Englands, Frankreichs und des 

 siidwestlichen Deutschlands,' correlates the English Upper Jurassics 

 with those of the Swiss Jura as in the accompanying table, p. 250 

 (extracted from his table no. 64). 



The classification employed by Oppel differs somewhat from that 

 which is adopted in this paper. His zone 34 includes the Yirgulian 

 and Pterocerian of later writers : zone 32 is the ' Oolithe corallienne 9 

 and the ' Calcaire a iN erinees : ' zone 30 is the Oxfordian ; and the zones 

 26-29 (inclusive) represent the Callovian, of which 27, 28, and 29 

 are the ' Per sous-oxfordien.' 



In the years 1857-60, Marcou's 1 Lettres sur les Eoches du Jura/ 

 &c, appeared, and in them he attempted, amongst other things, a 

 correlation of the Jurassic beds of the Eranche-comte with those of 

 England, and also refers to the same beds in the Jura. The only 

 beds which he correlates with certainty are included in his Groupe 

 corallien, which he makes the equivalent of the Coralline-oolite 

 Group of Phillips. All his other correlations are queried (see his 

 table, p. 101). 



"Waagen, in 1865, in his ' Versuch einer allgemeinen Classification 

 der Schichten des oberen Jura' (table, p. 30), gives the following 

 correlations of the English and Swiss beds. In the fourth column 

 the classification adopted in this paper has been added. 



s 2 



