A MONOGRAPH 



OF 



BRITISH CRETACEOUS BRACHIOPODA. 



PRELIMINARY REMARKS. 



In the present Monograph, our object is to describe those British species of Brachiopoda 

 that lived during the deposition of the widely spread and remarkable accumulation of 

 sediment known under the name of the Cretaceous System, the stratigraphical position of 

 which is between the lowest Tertiary and uppermost Oolitic deposits. 



The great character of the period is well marked by its animal remains, which are 

 abundant and often very perfect, owing to the nature of the sediment in which they were 

 imbedded. 



The active researches of a multitude of intelligent observers have shown, that the system 

 in itself is susceptible of being subdivided with advantage into periods of secondary value, 

 but far less important than those distinctions which separate the few great Geological 

 systems. Indeed, in many cases, the lines of demarcation in the subdivisions of a system 

 may be considered more or less arbitrary; forming links merely of a continuous series, as 

 is proved by some of the same species being common to each. These secondary divisions 

 are, however, good and useful as Geological horizons, and in most cases distinguished by 

 a prevalence of certain forms peculiar to each in particular, and having a more or less 

 prolonged existence. 1 



In Great Britain the Cretaceous System has a wide range. From Flamborough Head 

 on the Coast of Yorkshire it extends in a South-Easterly direction to the Wash in 

 Lincolnshire : commencing again on the North Coast of Norfolk, it proceeds in a South- 

 West direction, and occupies a considerable portion of the Counties of Norfolk, Suffolk, 

 Cambridge, Hertford, Oxford, Berks, Wilts, and Dorset. From the great central space of 



1 Consult Mr. Barrande's interesting paper on the " Migration of Species," • Bull, de la Soe. Geol. de 

 France,' vol. viii, 2d series, p. 150, 1851. 



