INTRODUCTION. 487 



Belgium, moreover, bears a general resemblance to the Scaldisien of that country 

 similar to that existing between those of the Coralline and Waltonian Crags. The 

 connection between the Coralline-Casterlien and the Waltonian- Scaldisien is as 

 clearly marked as the difference between those groups and the Miocene of 

 Antwerp. 



In his Pliocene Deposits of Britain, p. 222, 1890, the late CI. Reid identified 

 the Lower Red Crag (AValtonian) with the Astien of Piedmont, and the Coralline 

 Crag with the Plaisancien, placing the first in the Upper and the second in the 

 Lower Pliocene, but in the light of our present knowledge I cannot see any 

 sufficient reason for such a separation. The principal difference between the 

 Coralline and the Waltonian Crags is, that the latter contains a large number of 

 boreal species unknown from or exceedingly rare in the former, but the sudden 

 appearance of such shells in the Anglo-Belgian basin was due, 1 submit, to the 

 subsidence of the northern part of the area at that period, described in one of 

 my former papers,^ by which the Crag sea was for the first time brought, probably 

 somewhat suddenly, under the influence of marine currents from the north. 



THE LBNHAM BED. 



While agreeing with Mr. Newton that the Lenham fauna is older than that of 

 the Coralline Crag, I cannot consider it to be Miocene. I do not think that the 



Grammont 

 Tburnai 



Fig. 1. — Sketch map, showing' the connection between the Lenliani bod and the Diestien sands of Louvain 



and Diest (after Eutot).— P. W. H. 



list of Lenham fossils given and figured by him could, be taken by anyone 

 having a working knowledge of the subject for a typical collection of Coralline 

 species. 



Stratigraphically the Lenham bed is connected with the sands of Louvain and 

 Diest (zone d Terehmtula grandis of Van den Broeck) by a remarkable series of 

 isolated Diestien hills which form a curved line extending from west to east 

 through Folkestone, Calais, Cassel, Tournai, Grammont, Brussels and Louvain ; 

 beyond that region, as at Diest, these deposits cover the country with a continuous 

 sheet (see Fig. 1). 



The Diestien sands have been always regarded, as Pliocene by Belgian geologists, 



1 " The Pliocene Deposits of HoUaud," Quart. Journ. Geol. Soc, vol. Hi, p. 761, fig. 4, 1896 (see 

 also Fig. 3 of this work). 



