1909.] RECENT BIOLOGY OF SOME LIVING SHELLS. 751 



appears to me nearly conclusive, and it would seem to require us 

 either to revise the decision of Brogger and A. S. Jensen that the 

 shell does not occur in the Scandinavian raised beaches at all or 

 to put the Uddevalla shell-beds in a different category to all the 

 other raised beaches in the North, with the possible exception of 

 the Kadland bed, which is a quite possible solution. 



In some papers I have lately published in the ' Geological 

 Magazine ' on the recent history of the Baltic, I have ti-ied to 

 bring together the conclusions of the Scandinavian geologists on 

 the subject, with some additional views of my own. I will shortly 

 condense their main conclusions. The Northern geologists have 

 shown that the raised beds on the shores of the Baltic consist of 

 two entirely diflerent series, one containing marine shells and the 

 other freshwater and land shells only. 



The marine shells in these raised beds correspond to the present 

 marine fauna of the Baltic, except only that they show a change 

 in their range due, as is virtually certain, to the water of the sea 

 having become increasingly fresh. The typical shells in these 

 raised beds are two species of Littorina — Littorina litorea and 

 Littorina rudis, both of them greatly dwarfed. Hence they are 

 known as Littorina beds. 



The freshwater beds, which immediately preceded them in time, 

 are specially marked by the presence of Ancylus fluviatilis, and 

 are hence called Ancylus beds. 



The inevitable conclusion from the position and succession of 

 these beds is that the Baltic was formerly a great inland fresh- 

 water lake (the Ancylus sea) and in course of time was converted 

 into a brackish -water sea (the Littorina sea), which still subsists 

 although less saline than it once was. 



The accepted explanation of this change, a most reasonable 

 and inevitable one, confirmed by much evidence, is that after the 

 human period known as the Kitchen-midden period there w^as 

 a breach made in the land-bridge connecting Southern Scania 

 with Denmark and Denmark with Mecklenburg, by which the 

 Sound and the two Belts were opened, and the salt water of the 

 North Sea for the first time made its way into the previously 

 fresh Ancylus lake, converting it into a brackish -water sea and 

 supplying it with the marine fauna which now occupies it. 



The northern archaeologists on very reasonable data have roughly 

 calculated that the Kitchen-midden men lived some 8000 years ago. 

 Whether more or less, it follows that every raised beach in the 

 Baltic containing a marine or brackish-water fauna has been laid 

 down since the above-named breach took place. In other words, 

 the Littorina period in the history of the Baltic extends roughly 

 from 8000 years ago down to our own time. This means that 

 during the last 8000 years there have been great changes of level 

 in the Baltic lands involving their upheaval, and the elevation of 

 the highest of these shell-beds is a measure of the amount of this 

 elevation. They show that the movement has not been continuous 

 but differential, the highest recorded instance being at a height 



