500 HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



Sub-div. 4. About 40 feet of ferruginous clays for which 

 Thirria could not find an English equivalent. 

 (These were Tertiary deposits, erroneously 

 included by Thirria with the Jurassic 

 formation.) 



Sub-div. 3. Over 200 feet of rock corresponding with the 

 Kimmeridge Clay and Portland Stone, but 

 exhibiting in the upper horizons a lithological 

 and palseontological development different 

 from the English. 



Sub-div. 2. About 350 feet of rock corresponding with the 

 Kellaways Rock, Oxford Clay, and Coralrag in 

 England. 



Sub-div. i. About 270 feet of rock including five well- 

 marked horizons palaeontologically comparable 

 with the Inferior Oolite, Fullers' Earth, Great 

 Oolite, Forest Marble, and Cornbrash of the 

 English series. 



The memoir by Thirria was one of the best of the older 

 publications on Jurassic deposits, although it gave no 

 information regarding the tectonic structure of the area 

 examined. It was soon over-shadowed by the greatness of 

 Thurmann's tectonic and orographical studies in the western 

 part of the Swiss Jura mountains. The original ideas 

 formulated by the geologist of Porrentruy regarding the 

 processes of mountain-making have already been mentioned 

 (p. 302). In two memoirs, published 1832 and 1836, 

 Thurmann gave an admirable exposition of the stratigraphy 

 of the Bernese Jura. Voltz in Strasburg rendered willing 

 assistance in identifying the fossils and determining the 

 parallelism of the rocks with foreign equivalents. 



Thurmann distinguished the following sub-divisions in the 

 Terrain Jurassique : 



C. Upper Jurassic or Portland Group. 



15. Portland Limestone with Exogyra virgula, etc. 

 14. Kimmeridge Marl of Le Banne, very fossiliferous 



(Exogyra virgula ', Pteroceras Oceani, Mytilus 



Jurensis, etc.). 



