Alfred Belt — The Succession of the Crags. 211 



to have been ejected from a submarine cleft opening between Calais 

 and Diest, than to be an ordinary marine operation. He, however, 

 especially notices the tendency which the glauconitic grains have to 

 form nodular concretions. 



The richly fossiliferous black sands of Belgium and Holland rest 

 upon the Lower Miocenes, at but a slight elevation (if any) above 

 the sea-level; the ironsands, on the contrary, are never less than 

 180 feet above it. 



Now, assuming that the ironsands represent the in-shore and 

 shallower waters of the Diestien sea, the black sands would also 

 represent the deeper. It is then obvious that when the elevation of 

 the Wealden dome exposed the upper sands to the action of the 

 currents flowing from Normandy to the North Sea, the easily 

 decomposed sandstone would be destroyed, whilst the harder 

 nodules would be carried over the sea-bottom.^ When in process of 

 time, the lower black sands were brought into the same range of 

 action, they would be likewise denuded, and their Molluscan contents 

 removed, and carried with the nodules into the later Red Crag sea. 

 I can find no easier hypothesis to account for the presence of so 

 many Black sand shells in the Red Crag and not in the Coralline.^ 



Which of the oO or 60 Cetacea are proper to the black sands, is 

 uncertain, and the same with the Mammalia ; but from present 

 evidence, they are quite as likely to be of the age of the deposits 

 they occur in as not. 



Before passing to Mr. Prestwich's memoir^ I may remark, that as 

 the Belgian "Sables gris" contain shells, which in England do not 

 occur in the Coralline Crag but only in the Red Crag, the presumption 

 is, that they are either immediately posterior in date to the Coralline 

 Crag, or belong to its latest development. Amongst these are 

 Melampus pyramidalis, Fusiis elegans, F. antiquus, Littorina suhaperta, 

 Cardium ParTcinsoni, Tellina lata, etc. M. Nyst informed me, when 

 looking over his collection at Brussels, that he then considered the 

 Sables Jaunatres to be of the same age as the Sables gris. The fauna 

 is almost the same, and is exactly that of the English Middle (or Red) 

 Crag. The Upper Crag (of A. and R. Bell) does not obtain in Belgium, 

 but appears near Dordrecht, in Holland, as there we meet Nucida 

 CobboldioB, Leda limatula, and others. 



The sum of Mr. Prestwich's argument seems to be as follows. 

 That the whole series of English Crags are divisible into two — the 

 Coralline and the Red Crags ; the latter being again divided into two 

 divisions, the lower comprehending all the beds hitherto denominated 

 Red and Norwich Crag, the upper the Chillesford sands and clays 

 covering the whole, Coralline Crag included.^ 



1 That is the Coralline Crag sea 



^ Six or eight Pleiirotomas, including, P. turricula, Broc, F. intorta, a large Mitra, 

 one or two Volutes, a Cassis, Ranella anglica, Murex exculpta. JVassa cmiglobata (?), 

 Tellina Benedenii, etc., perhaps twenty in all. Also Solenustrva Frestu-ieliii, and a 

 tolerably common Flabellum (? n.so.). 



3 The division into zones of the Coralline Grng is of much viilue, hut from my own 

 investigation, I think some of the zones, considered as separate, really are concurrent 

 with each other. Thus at the Gomer Pit, 1 found the zone / included the fossils of 

 zone d, tlie larger shells immediately underlying the zone containing the smaller. 



