the Limits of the Jurassic and Cretaceous Periods. 331 



The following, it seems to me, is the mode in which we may 

 sum up the concordant portions of the documents above cited. 



Leaving on one side, for reasons already indicated, the stages 

 of Provence, Mont Saleve, and Wimmis*, and applying what 

 follows only to countries in which the Tithonian stage is well 

 developed, we find in ascending order : — 



1 . The fauna of Ammonites tenuilobatus ; 



2. The fauna of the Lower Tithonian, represented especially 

 by Rogoznik, the blue marble of the Apennines, and probably 

 by the limestone with Terebratula diphya of the Tyrol ; 



3. The fauna of the Upper Tithonian, or Stramberg limestone 

 (Tereb. janitor); 



4. The Lower Neocomian stage, and particularly the limestone 

 of Berrias (Tereb. diphyoides). 



Nos. 1 and 2 have dominant Jurassic characters; No. 3 is 

 rather cretaceous ; No. 4 has most of the normal characters of 

 the latter epoch. 



Those who seek for the line of separation between the two 

 great periods place it now between Nos. 2 and 3. The perforated 

 Terebratula, then, give the following result : the Terebratula 

 with a small aperture (T. diphya, Catulloi, &c.) belong to the 

 most recent Jurassic deposits ; the Terebratula with a large aper- 

 ture (T. janitor and diphyoides) are Cretaceous. 



But this solution, which is apparently so simple, raises a great 

 question, almost identical with that which we indicated above. 

 The four stages above cited are bound together by great palseon- 

 tological analogies. Several species incontestably pass from 

 No. 1 to No. 2, from this to No. 3, and from No. 3 to No. 4. 

 *Nos. 2 and 3 especially, which would be separated by the line of 

 demarcation of the periods, have about one-third of their species 

 in common. This line would therefore be a very weak boundary, 

 and we should have to admit that in this Tithonian basin the 

 separation of the Jurassic and Cretaceous periods was singularly 

 compromised. 



In the presence of such a result, so much opposed to generally 

 received notions, we can only repeat what we have said in previous 

 works. Let us wait for fresh facts, and suspend all definitive 

 judgment until we become acquainted with new sections, and 

 new local faunas can be adduced to confirm or invalidate what 

 our present results seem to force upon our acceptance. 



We may especially hope soon to have a satisfactory description 



* These coralline limestones of Wimmis and Mont Saleve belong, as I 

 have already said, to the Upper Jurassic, and are in all probability the equi- 

 valents of the Inferior Tithonian stage. A good palaeontological investiga- 

 tion is indispensable before we can appreciate their precise relations with 

 the Tithonian stage of the Voirons, of Chatel-Saint-Denis, &c. 



