206 



M. J. Thtjemann, * iu his admirable essay, "siu* les souleve- 

 mens Jurassiques du Porrentruy," has described the Oxfordien 

 group in the Jura as it exists in Mont-Terrible. The division 

 and palseontology of these beds agree substantially with the 

 condition of things existing in the departments of France, just 

 described. 



M. Jules Marcou f has contributed a most valuable memoir 

 on the Jura salinois, in which he has described the physical 

 and biological contents of the Jurassic rocks in the Franche- 

 Comte. The same learned author has, likewise, in a later 

 publication, a series of letters to my late friend Professor Oppel, 

 compared the synchronism of the middle and upper Jura 

 franc-comtois with corresponding formations described in the 

 memoirs on the Haute-Saone, by M. Thirria; the Cote-d'Or, 

 by M. de Nerville ; the Haute-Marne, by M. E. Eoter ; the 

 Meuse, by M. Ed. Piette ; the Moselle, by MM. Teeqtjem and 

 PiETTE ; the Ardennes, by M. Piette ; the Cevennes by MM. 

 Em. Dumas and Paul de Eouville ; and the lower Jura with 

 the works of different English authors, — Professor Phillips, 

 Mr. Edward Hull, and Dr. Wright. 



Dr. William Smith long ago divided his Clunch, or Oxford 

 Clay, into the argillaceous strata, or Oxford Clay proper, 

 forming the great mass of the formation and including sub- 

 ordinate beds of yeUow sandy Limestone, which he first found 

 at KeUoway Mill, Wilts, and which he called Kelloway rock. 

 Subsequent discoveries have proved that the distinction was 

 correct, and that a classification of the upper beds of the group 

 may be made by a critical study of their organic remains. 

 Keeping steadily in hand the key that has helped us to unlock 

 the sub-divisions of the Lias and Lower Oolites, let us proceed 

 with the beds of the middle oolitic formations. 



Many years ago, during the construction of the Great 

 Western Railway between Chippenham and Trowbridge, the 

 lower beds of the Oxford Clay down to the Cornbrash were cut 

 through, and an immense number of Ammonites and other 



* Memoires de la Soc. d'Hist. Naturelle, de Strasbourg : 1832. 



t Eecherches geol. sur le Jura salinois, Mem. Soc. geol. de France : 1846. 



