Sir H. H. HoivortJi — Geological History of the Baltic. 453 



In Brogger's admirable inonograpli on the molluscs of the raised 

 beaches in the Christiania Fjord he has compared the living fauna of 

 tliis great Norwegian bight or inlet with that in the later raised 

 beaches of Norway, and has shown that a certain number of the 

 molluscs now found living in Norwegian waters are not found in 

 these beaches at, all, and he very naturally infers from this tliat they 

 have invaded these waters since the latest beaches were deposited, 

 a large proportion of them having probably come as a direct or 

 indirect consequence of human effort. 



It is interesting to analyse these immigrants. Pive of them 

 which seem to thrive and flourish in the temperate waters of the 

 Christiania Fjord belong to the highest latitudes. They are Acmcea 

 testudinalis, Lophyrus albus, Scalaria Groenlandica, Cerithiopsis 

 costulata,^ and Nucula delpliinodonta.' The notable thing about 

 these five high Arctic shells is that not only are they not found in 

 either of the two sets of raised beaches in the Christiania Fjord, they 

 are also not found on the Arctic shores of Northern Asia from the 

 Kara Sea eastwards, but occur abundantly in the Arctic lands of the 

 New World from Behrings Straits to Greenland, and Brogger lias no 

 hesitation in treating them as Nearctic shells which have migrated 

 in late historical times to Europe, having, not improbably, been 

 transported by whalers and seal-fishers. The notable thing to 

 remember about them is that they seem to thrive under such new 

 conditions. 



We will now turn to a number of Boreal species which have, 

 probably, found their way into the Norwegian waters in recent years, 

 notably: — ^^ 



Mya arenaria (of whicli we have spoken above), Tellina pusilla, Macoma 

 tenuis, Psammohia tellinella, Bwpicola distorta, Necera rostrata, and Bisso- 

 stomia octona, all recent introductions from the West. 



Lastly the LusiTANiAjsr species, which have immigrated since the 

 latest raised beds were laid down, viz. : — 



Lima hians, Modiolaria mar'niorata, Nucula nitida, Sphcenia Binghami, 

 Teredo navalis, Trochus zizyphinus, Hydrobia ventrosa, Onoba costata, 

 Cingula semistriata, Turbonilla scalaris, Stilifer Turtoni, Mangelia attenuata, 

 M. striolata, Scalaria Turtoni, Aplysia punctata. 



It is not possible to know how these vagrants found their way into 

 Scandinavian waters during a period when the climate, as we shall 

 see presently, has been only slightly changed, nor would a change of 

 climate avail as a reason, for the newcomers belong to different 

 marine climatic regions. In regard to the Lusitanian migrants 

 I have a theory which I think interesting, but must postpone to 

 another paper. 



From these recent comers we will turn to the shells which are 

 found in the later raised beaches, but no longer live in the neigh- 

 bouring sea. The total number of shells from these beaches is 255. 

 Forty of these are Arctic, 103 Boreal, and 112 Lusitanic. Of these 

 210 are now living, leaving 45 species represented in the beaches 



^ This species, which does not occur in the beaches of the Christiania Fjord, 

 has been found in those at Uddevalla and in Britain. 



