Sir H. H. Hoiuorth — Geological History of the Baltic. 459 



living there. Not only so, but it is plain that whenever and where- 

 ever tliey lived they were surrounded by Arctic conditions. This is 

 indisputable. What I dispute is that they in any way testify to 

 a Glacial period. If they did so, that Glacial age must have inter- 

 vened between the period when the Tapes beds were uplifted and the 

 present conditions of climate in the Scandinavian seas, which 

 biologically are duplicates of each other. This would mean, first, 

 that the postulated Glacial period was intercalated between two 

 periods marked by tlie same temperate marine fauna. In other words, 

 the fauna of the Tapes beds must have been entirely exterminated by 

 the extreme Arctic climate of the Yoldia period, and then the latter 

 must in turn have been similarly exterminated and replaced by the 

 older inhabitants, after which a return to precisely the same 

 conditions a<iain took place. 



Apart from all other considerations, the proposed theory involves 

 not merely a gradual change of climate, but a sudden and drastic 

 one, or else there would be some evidence of a gradual transition of 

 fauna, whereas there is none, but a complete and drastic change of 

 the whole fauna. Secondly, there is the puzzle of explaining 

 whither the remnants that escaped the extermination fled, and 

 whence they could return to their old homes in better times. 



Surely such a position is preposterous and unbelievable unless 

 supported by overwhelming evidence. As a matter of fact, 

 Dr. Brogger produces no evidence at all, but only a quite fallacious 

 deductive argument. He says quite rightly that in the high 

 Arctic sea where the Yoldia and its companions are found, they 

 mostly live at a depth of from 10 to 30 metres, a number of them, 

 he adds, living at greater depths (op. cit., 681). He then goes on 

 to argue that the same species of molluscs when it lived in the 

 Scandinavian seas must have lived at about the same depths, 

 notwithstanding the great difference in latitude. To justify the 

 immense postulate he relies on the still more wilful one of a Glacial 

 nightmare as his deus ex machina, and entirely ignores the two 

 fundamental difficulties I have just pointed out. 



It seems to me that a very much more simple explanation of the 

 phenomena we are discussing is available which needs no fantastic 

 postulates to support, but only an accurate induction from the known 

 facts. I would urge in answer to Dr. Brogger that what the Yoldia 

 and its companions require for their existence is not a uniform 

 depth of water in all latitudes where it lives, but a fairly uniform 

 temperature in the water. That temperature exists now not only in 

 the Arctic Circle but in the depths of the Atlantic and of the North 

 Sea, and needs no Glacial nightmare to create it in those latitudes. 

 It has not truly been proved to do so by a great many deep-sea 

 soundings, and it is an inevitable corollary from the interchange of 

 warm and cold water between the temperature of Arctic regions as 

 a result of natural laws of ocean circulation. 



We all know the elementary example which has been so often 

 quoted, namely, tlie existence of living northern molluscs, not only 

 in the b ireal latitudes of Ghristiania, but in tlie southern one of the 

 Mediterranean. These molluscs do not occur there at the same depth 



