Correspondence — Mr. W. T. Blanford. 47 



The '■' Martinez group," also quoted as Cretaceous, is only a sub- 

 division, composed of a few passage-beds without real value, and 

 ought to be dropped. 



Then comes the " Tejon Grroup," vphich Mr. Starkie Gardner 

 admits as being Tertiary without question. 



The Cretaceous series of North America are far more complete 

 than represented in Mr. Gardner's paper ; for he has overlooked 

 entirely the Cretaceous rocks of Texas and the Lower Mississippi 

 basin. The expression of " Lower Cretaceous " of America, as used 

 by him, is misleading, for it means only the lower parts of the Cre- 

 taceous rocks of the basin of the Upper Missouri, where neither the 

 Lower Cretaceous or even the Middle Cretaceous of Europe are 

 found. It is even very doubtful if there is a representative of the 

 Marly Chalk {craie tvffeau de Touraine) or "Turonian." 



The " Dakota and Fort Benton gi'oups " represent with their fossils, 

 such as Ptijcliodm and other fishes, Inoceramns, etc., the White Chalk 

 of Sens or " Senonian " ; and certainly are not older than the lower 

 jDart of the Upper Cretaceous rocks of England and France. All the 

 upper divisions, called " Fort Pierre and Fox hills groups," are the 

 representatives of the most upper part of the European Cretaceous 

 rocks called " Danian," and which exist at Maestricht, Aix-la- 

 Chapelle, Ciply near Mons, Faxoe in Denmark, in Provence, and 

 the Pyrenees. 



The " Laramie group " represents the lower part of the European 

 Eocene from the Pisolitic limestone of Paris, the Meudon clay, the 

 Eilly limestone, the Paris Plastic clay, the Puddingstone of Nemours, 

 the Soissonnais sands, the beds of the Isle of Thanet, as far up as the 

 Middle Eocene of Sir Charles Lyell. It represents and corresponds 

 to the "Chico group" ef California. 



And because Mosasaurus exists in the Laramie, that does not make 

 it Cretaceous, any more than the existence of the degenerated 

 Ammonites and BacuUtes Chicoensis at Chico Creek makes the " Chico 

 group " Cretaceous. But it only shows that Mosasaurus, Ammonites, 

 and BacuUtes existed in America at the beginning of the Tertiary 

 period, when they had already finished their existence in Europe. 



Cambridge, Massachusetts, United States, Jules Marcou. 



November Vlth, 1884. 



THE CLASSIFICATION OF THE JUKASSIC SYSTEM. 



Sir, — I am indebted to Mr. A. J. Jukes-Browne's letter in the 

 Geological Magazine for last November, for an opportunity of 

 explaining my reason for proposing, in my note on the Classification 

 of Sedimentary Strata, to draw the line of division between Upper 

 and Middle Jurassic above the Oxford Clay. 



I mentioned in my note that this was a doubtful question, and the 

 weight of authority is in favour of Mr. Jukes-Browne's view, that 

 is, of classing the Oxford Clay as Upper Jurassic, though many con- 

 tinental geologists consider the Kelloway Rock (Callovian) as per- 

 taining to the Middle series, owing to the German equivalent belong- 

 ing to the Dogger or Brown Jura. At the Zurich meeting ol the 



