Sir H. H. Howorth — Geological History of the Baltic. 455 



water due to the outflowing of so much fresh water from the Baltic, 

 which certainly destroyed some, may have had a wider influence 

 than we know. Another cause to which we will turn presently is the 

 great shallowing of the water in certain cases, and a third a possible 

 change of the temperature of the water affecting the supply of food. 

 What is important to remember is that the mollusca represented by 

 the so-called post-Glacial beds belong essentially to that of the 

 Tapes beds of the Cattegat beaches, and that although Tapes is 

 extinct in the Christiania Fjord, two species of the genus are no 

 longer found there, but are still found living in the North Sea and on 

 the Western Norwegian coast. Dr. Brogger, in fact, as I have said, 

 calls the greater number of the beds occurring in the Christiania 

 Fjord, which he classes as post-Glacial, the Tapes beds. 



I would venture very deferentially, therefore, to differ from him 

 in allocating anything more than a quite relative value to the 

 presence or absence of any particular shell from a bed as a test of its 

 age or homotaxis. I would treat them as the result merely of 

 different local surroundings and as being entirely local divisions, and 

 in this case I would name them all Tapes beds, and use that name 

 in the sense in which Dr. Brogger uses the name post-Glacial beds. 



-Turning to these later or so-called post-Glacial beaches in the 

 Christiania Sound, 1 will give a list of some of their heights above 

 sea-level as reported by Sars (op. cit., p. 3) : — 



On the east side of that Gulf. Heights above sea-level. 



To each of these numbers Sars would add 90 feet in order to ascer- 

 tain the actual depth at which the molluscs live. 



Let us now turn to the high Arctic beds, which have a good deal 

 more importance and interest for us than the later or post- 

 Glacial ones. 



I have stated that in the Christiania Fjord and in the northern 

 part of the Cattegat, in addition to the Tapes beds which occur at 

 different levels, we have another series unmistakably contrasted with 

 them, since they only contain shells belonging to an extreme Arctic 

 type, while on the other hand the two sets of beds have none of their 

 shells in common, so that in dealing with them we get rid of all 

 the difficulties of overlapping. These beds have been called from 

 their most characteristic shell Toldia clavs. They present some 

 critical problems in which I find myself in sharp difference with the 

 Northern writers. 



The fauna of these beds comprises the following twenty- six species 

 of molluscs and a number of varieties. 



