2 BRITISH CRETACEOUS BRACHIOPODA. 



Salisbury Plain it takes an Easterly direction, by Andover, Alton, Guildford, Reigate, 

 Wrotham, Rochester to Ramsgate, Deal and Dover, on the East Coast of Kent. In 

 another direction, from Salisbury Plain, it proceeds by Winchester, Arundel, and Lewes, to 

 Brighton, Newhaven, and Beachy Head on the Channel. It also passes through the 

 centre of the Isle of Wight, from the Culver Cliffs and Needles at the Western extremity, 

 occupying a large part of Hampshire, and greater or less portions of Surrey, Sussex, and 

 Kent, by those two Southern divisions of its course. Chalk also occurs in the North of 

 Ireland; but, for further details, we must refer to those excellent Geological works, in which 

 every stratigraphical detail will be found admirably delineated. 1 Therefore we only mention 

 here a few points connected with the distribution of our species. 



In Great Britain the Cretaceous System is incomplete : some of the lower beds are 

 wanting, such as the lower Neocomien of the French. The total thickness of our beds is 

 supposed to be from 600 to 1000 feet, divided by the generality of British Geologists into 

 six subdivisions, varying more or less in their mineralogical composition, but not all equally 

 well denned by their organic remains ; at least so far as Brachiopoda are concerned, as 

 may be observed during the progress of this work. In the red chalk of Norfolk three 

 species only have been noticed as yet, one common in the Lower Chalk, the second in the 

 Upper Green Sand and Gault, and the third has not hitherto been discovered in any other 

 British deposit, but is peculiar to the Tourtia of Belgium. Geologists seem to consider the 

 red chalk to represent the Gault, from its being said to contain other species, such as 

 Am. dentatus, Bel. minimus, Inoceramus sulcatus, and some other forms common to that 

 strata. But few species are found in the Speeton Clay, these also occurring in the Upper 

 Green Sand of Cambridge : most Geologists have considered the Speeton Clay as the 

 equivalent of the Gault. We therefore believe it possible that the Upper Green Sand and 

 the Gault are more intimately connected than is generally allowed. In the true Gault, few 

 species are met with; those conjectured from the Gault of Cambridge turn out to be all 

 from the Upper Green Sand. 



The age of the Farringdon beds may yet afford a subject of discussion, although 

 several distinguished geologists 2 state them to be Lower Green Sand. All I can say is, 



1 Consult the works of Messrs. Smith, Conybeare, and W. Phillips ('Outlines of the Geology of 

 England and Wales,' 1822) ; the various papers and works of Dr. Fitton, in the ' Geol. Trans.' and 'Quart. 

 Journ. of the Geol. Soc. ;' Professor Phillips ('Geol. of Yorkshire') ; Sir II. de la Beche ('On the Chalk 

 and Green Sand of Lyme,' &c), 'Geol. Trans.,' vol. ii; Dr. Mantell's several works on the ' Geology of 

 Sussex,' in 1822, 1833, and 1844. Also the interesting papers of Professor Forbes, Messrs. E. Bennet, 

 Lonsdale, Rose, Woodward (' Geol. of Norfolk'), Morris, Weaver, Clarke, Bowerbank, Lyell, Ibbetson, 

 Austen, &c. Also the works of many distinguished foreign geologists, such as Viscount d'Archiac, 

 D'Orbigny, Reuss, Rcemer, Cuvier, Brongniart, &c. &c. 



2 Refer to Mr. Austen's paper in the ' Quart. Journ. of the Geol. Soc.,' vol. vi, No. 24, p. 454, 1850; 

 likewise, for the position of the Mans beds, to M. E. Gueranger's interesting section in the 'Bull. Soc. Ge'ol. 

 de France,' vol. vii, 2d ser., p. 800, 1850; also to Viscount d'Archiac's 'Memoir on the Tourtia,' in the 

 'Mem. de la Soc. Geol. de France,' vol. ii, 2d ser., p. 293, 1837. 



