1909.] RECENT BIOLOGY OF SOME LIVING SHELLS. 759 



the English seas can he followed step by step and year by year ; 

 and it is a most eloquent fact that while Mya arenaria abounds 

 in the present Wash, it does not occur, like the other shells from 

 the same estuary, in the beds deposited in the immediately 

 preceding period, and is very strong evidence of the recent 

 addition of the mollusc to the fauna of the Eastern Coast. 



This English evidence may be paralleled by that of Belgium. 

 Thus Dr. Raeymaekers, who describes its common occurrence on 

 the shores of the Low Countries, notably at Ostend, Heyst, and 

 Blankenberg, speaks of it as a recent immigrant. " Malgr-e toutes 

 nos recherches," he says, " nous n'avons pu decouvrir Mya arenaria, 

 L. dans les depots superieurs a la tourbe. Aucun des geologues 

 qui ont public des travaux concernant les terrains quaternaires 

 d'Anvers n'a signale la presence de cette espece dans les forma- 

 tions modernes ; celle-ci ne devait pas encore avoir apparu dans 

 ces parages." He then describes a recent excavation made near 

 Kruyschaus, not far from the redoubt of Oorderen, where he 

 carefully studied all the layers above the turf (tourbe) : " Malgre 

 d'actives recherches, nous n'avons pu y trouver des exemplaires de 

 Mya arenaria dans la tourbiere encore ouverte ; au nord au dessus 

 de Doel, nous n'avons pas ete plus heureux." 



In the turf, he says, there are argillaceous sands, very damp 

 and containing ti'unks of trees and shells of Cardiuin edule, 

 Scrohictdaria j)i2)erata, and Tellina baltica, and then the so-called 

 Polder clay, but no traces of Mya arenaria, and he concludes : 

 " Pour notre part, nous croyons que I'epoque de I'apparition de 

 Mya arenaria L. ainsi que la date de sa disparition du Bas Escaut 

 sont relativemeiit recentes et posterieures a la periode espagnole." 



Dr. Raeymaekers further showed that the sand covering the 

 ditches at Lille rests on the Polder clay. These ditches he proved 

 were made at the same time as the fortress of Lille, and could be 

 emptied or filled at will by a series of sluices. The sand in 

 question, a thin layer, contains shells of Mya arenaria so fresh 

 that their epidermis is still preserved, as is the ligament uniting 

 the valves of the Cardinm edide. In the war of 1830 the Dutch 

 opened the sluices and the country north of Antwerp was 

 inundated. This continued till 1849-1850, when the Polders 

 were again laid bare and cultivated, and it was during these 

 twenty years that the Myas had invaded the ditches, thus explain- 

 ing their being now found in dry ground and otherwise so fresh 

 (Annalesde la Societe Malacologique de Belgique, xxx. pp. 5-11). 

 The evidence, therefore, is very consistent and complete that 

 they have only come to the shores of Belgium in recent times. 



If we turn from these estuarine silts, the next deposits we 

 come to ax^e the raised beaches. Raised beaches do not, of course, 

 occur on coasts which are being eaten back by the sea. We 

 do not, therefore, find them on the east coast of England any 

 more than on the western coast of Jutland. They do occur, how- 

 ever, in numerous places on the south and south-west coasts of 

 this island, and afford good evidence that these coasts have not 



