BRITISH TERTIARY BRACHIOPODA. 



Terrains Tertiares . 



^27. Subapennin, 



26. Falunien, 



25. Parisien, 



24. Suessonien, 



to avoid the Cenes, as lie declares to have found the identifications of the recent Eocene 

 species inexact, and not existing in the recent state. Without wishing to decide the 

 question of who is right, and what names should be adopted in preference to others, we 

 shall admit three great divisions, Lower-, Middle, and Tipper, each liable to subdivision, as 

 shown by Sir C. Lyell, D'Archiac, and other authors. The important facts lately brought 

 to light in the arrangement of the lower division, are mainly due to the zealous and 

 indefatigable researches of Mr. Prestwich, 1 that author having established that the Barton 

 clays and Braklesham sands were the equivalents of the French Glauconic Grossiere, or 

 lowest beds of the Calcaire Grossier, while tha London clay and Bognor rocks represent 

 the French Sables Inferieurs, and Lits Coquittiers. The Middle Division, or Miocene, 

 appears wanting in our island, and therefore we will not allude to it, but mention that the 

 Upper Division, or Pliocene, is well represented in our island, and may, like the other 

 great divisions, be subdivided into distinct periods. This upper division, comprising our 

 newest Tertiary Deposits, is composed of sands, gravel, irregular beds of limestone, and 

 layers of greenish marl, known by the name of Crag. These have been divided into three 

 sub-divisions, viz., the Coralline, the Bed, and the Mammaliferous Crags. 



Some Geologists place the Coralline and Red Crag in the Miocene periods, and the 

 upper crag in the Pliocene. 2 Others have separated the two lower crags, placing one in 

 the Miocene and the other in the Pliocene; 3 and lately, 4 the two lower crags have been 

 considered as belonging to one period {older Pliocene), and the upper or Norwich crag 

 {newer Pliocene). 



Mr. S. Wood objects, however, to this arrangement, now considering the crags to 

 belong to three distinct periods ; so that,' by subdividing the newer Pliocene into lower 

 (Coralline Crag), medial (Red Crag), and newer (Norwich or Mammaliferous Crag), we 

 would be nearer the probable state of things as far as our island is concerned. 



I have deemed it necessary to enter into these few details in order to explain the reasons 

 why we arrange the different species contained in this Monograph more in one period than 

 in another. 



For more ample details on the Geology of this system, we would refer to the works 



1 'Quarterly Journal of the Geol. Soc.,' Nov., 1847. 



2 See Viscount d'Archiac's ' Histoire de Progres de la Geologic de 1834 a 1845,' vol. ii, 2de partie, 

 p. 447, &c, 1849. 



3 See S. Wood, 'Monograph of the Crag Mollusca,' Introduction! 1848. (Mr. S. Wood is now, 

 however, of a contrary opinion, placing all the Crags in the newer Tertiaries.) 



Also formerly by Sir C. Lyell. 



* Sir Charles Lyell, 'A Manual of Elementary Geology,' p. 362, 1851. 



