486 PLIOCENE MOLLUSCA. 



It is true that in 1848 in the Introduction to the first part of his Monograph 

 of the Crag Mollusca, following the ideas then current, Wood expressed the 

 opinion that the Coralline Crag might be of Miocene age,^ but two years later, in 

 his second part of 1850, that view was withdrawn," and no attempt has been made 

 since, either in this country or abroad, to revive it. 



Four hundred and thirty species of marine Mollusca were reported by Wood 

 from the Coralline Crag in his synoptical list of 1874.^ Of these only about 90, 

 21 per cent,, were known at that time from Walton, but even then he had come 

 to the conclusion that there was a close and general connection between the 

 two deposits.* 



The subsequent investigations of Prof. Kendall and the late R. G. Bell at 

 AValton, and my own at Little Oakley have strongly supported Wood's later 

 opinion. Of the 430 Coralline Crag species referred to, 270, or about 64 per 

 cent., are now known from the Waltonian or from some later horizon,^ while 

 hardly any of the rest can be considered as common or representative Coralline 

 Crag forms. To regard a species of which only one, or at the most a very few 

 specimens, have been obtained during the labours of a century, as of equivalent 

 value for purposes of analysis to others of which a large number could be found 

 at any time in a few hours, is misleading. It is by the general facies of a fauna — 

 by the abundant and not by the rare examples — that we should be guided. 



While, therefore, nearly all the more characteristic Coralline Crag species 

 continued to exist in the Anglo-Belgian basin during Waltonian times, or even to 

 a later period, no such correspondence can be traced between the Coralline Crag 

 fauna and that of the Belgian Miocene of Antwerp. Out of 230 species of 

 Mollusca reported from the latter," only 106, or 46 per cent., are known from the 

 Coralline Crag, the rest being generally and distinctly of an older type. 



The true Belgian equivalent of the Coralline Crag is the zone a Isocardia cor 

 of Van den Broeck, for which I have revived his name, Casterlien, the fauna of 

 the two being practically identical. Of about 150 species from the latter recorded 

 by that authority^ and by M. Bernays,^ all but about half-a-dozen have been 

 obtained from the Coralline or the Waltonian horizons. The Casterlien fauna of 



^ Mon. Crag Moll., pt. i, Introduction, p. v, 1848. 



2 02). cit, pt. ii, p. 302, 1850. 



3 Op. cit., 1st Suppl., pt. ii, p. 203. 



■* In the 4th ed. of his Antiquity of Man (p. 250, 1873), Lyell quoted Wood's opinion that 

 the Walton bed had an essential affinity with tlie Coralline Crag. 



^ The discovery by Alfred Bell in the Coralline Crag of Boy ton of some typical Eed Crag species 

 such as Nassa reticosa, unknown from the Gedgrave horizon, tends still further to connect the latter 

 with the Walton beds (see Journ. Ipswich Field Club, vol. iii, pp. 11, 15, 1911). 



fi Ann. Soc. Malac. Belg., vol. ix, pp. 118, 134, 1874. 



7 Op. cit., p. 187. 



8 Bull. Soc. Beige Gcol., vol. x, Mem., p. 128, 1896. 



