748 SIR HENRY H. HOWORTH ON THE [ISToV. 9, 



Giol, and on the south coast of the island of Oeland, in two 

 instances only out of twenty-nine citations of beds from the 

 broader part of the fiord did the shell occur. In both cases at 

 the sea-level. Lastly, at Korsholm, south of ISTormandshage, an 

 island situated in the mouth of the Limfiord, where it opens into 

 the Oattegat, and subject therefore to considerable wave-action, the 

 Mya occurred in a beach now being formed from the sea-level up 

 to 1"3 metre in height. This was the only case out of eleven 

 similar deposits quoted where the Mya occurred. 



It is plain that in all these four cases the deposit may really 

 have taken place within a few years only, and that it has done so 

 cei-tainly since any alteration in the level of the land has taken 

 place. 



Turning from the Limfioi-d to Wendsyssel, we have a more 

 notable occurrence of the shell and one showing how easy it is in 

 these matters to be misled. This was also originally published 

 by Jessen in 1899, in the first volume of the Records of the Danish 

 Survey, Raekke 3, p. 279. He mentions finding the Mya arenaria 

 south-east of ISTabstjert, in the south of Wendsyssel, at a distance 

 of 300 metres from the present sea-shore, and at a depth of 0"6 of 

 a metre under the sea-level. 



Professor Brogger seems to have attached rather more import- 

 ance to this discovery as qualifying his views of the quite i-ecent 

 arrival of the shell in these seas than it deserved, for in the later 

 memoir already quoted, and published in 1905, Jessen points out 

 that in comparing the map of this district published by the General 

 Stafi" in 1883 with other maps dating from 1785-1787, it becomes 

 clear that the coast has greatly altered here by silting, and that 

 in the course of 100 years it has advanced 300 metres at Aalback, 

 north of Nabstjert, while the mouth of the river Jervip, south of 

 Nabstjert, had advanced eastwards 600 metises (Jessen's Memoir 

 on the geological map of Aalborg and Nibe, noi^thern ]3art, p. 158 

 note). This shows that all the discovery at Nabstjert proves is, 

 that Mya arenaria was living on the northern coast of Jutland a 

 century and a quarter ago, for the place where it is now found at 

 300 metres inland was then in fact on the shore. 



The Danish evidence, therefore, is perfectly consistent with 

 that of Sweden in regard to the fact that the Mya arenaria, which 

 now so abounds in both areas, is quite a recent addition to their 

 marine Mollusea, and has only lately entered the Baltic, the 

 Oattegat, of which the Limfiord is a mere inlet, and the Belts. 



Let us now tvirn to Norway. Mya arenaria, according to Sars, 

 now occurs living on all the Norwegian coasts from the Christiania- 

 fiord to the North Cape. It has also been reported from the 

 warmer part of the White Sea. Professor Brogger is strongly of 

 opinion, however, that as in Sweden and Denmark so in Norway, 

 the mollusc is a recent ai-rival, a conclusion he bases on its absence 

 from the raised beaches. (Brogger, " Om de senglaciale og post- 

 glaciale NivSfortindringar," Norges Geol. Unders., N. 31, p. 605.) 



Sars, who in 1863 had claimed that it occurs in a raised beach in 



