464 Proceedings of the Royal Irish Academy. 



marine shells in this deposit throughout almost the "whole of Eussia, 

 and the fact that the boulders from Scandinavia evidently travelled 

 steadily in a south-easterly direction for a considerable time. 



The peculiar conditions of the physical geography of Xorth em Europe, 

 viz. the complete isolation of the cold Arctic from the warm Atlantic 

 waters, must have produced an excessive precipitation on the Scandi- 

 navian mountains in the foim of enow (see map, p. 461). Glaciers were 

 formed abundantly on these mountains, as the snowfall during the 

 winter months must have exceeded the amount of snow dissolved 

 during summer. On the west coast of Scandinavia they seem to have 

 hardly reached the sea, as was pointed out by Sir Henry Ho worth (40 a, 

 p. 709), but on the Swedish coast icebergs were detached from the 

 glaciers as soon as they readied sea-level. As the current at first 

 flowed from north-east to south-west, the icebergs travelled in that 

 direction, and many were stranded, as we know from the occurrence of 

 Scandinavian boulders in the British upper Pliocene deposits, on the 

 east coast of England. When the level of this Xorth European Ocean 

 rose to a sufficient height to join, by means of several straits, the 

 Ponto-Caspian Sea, a current would naturally flow in that direction, 

 as I have already explained (p. 456). We have evidences of this 

 current in tlie so-called Glacial striae which are occasionally visible 

 on the underlying rock. Prof. Geikie teUs us (35 a, p. 474) that in 

 Finland, and the adjacent tracts of Russia, two systems of Glacial 

 striae are apparent. The striae of the older system run in parallel 

 directions, and extend far east and south-east of the terminal moraines, 

 the younger system crossing the other at various angles. Again 

 (p. 426), he remarks : " At Eiidersdorf (Berlin), there are two set« of 

 striae, one set trending towards south-east, the other and later series 

 being directed towards the west." In speaking of the boulder-clay of 

 Iforthern Germany generally, he says (p. 463) : " There is usually a 

 well-marked distinction between the boulder-clays of the lower and 

 upper diluvium. The former are generally tougher and more abun- 

 dantly crowded with stones and boulders — the colour of the clay 

 being often dark gray or grayish-blue. Moreover, the included 

 erratics have travelled in directions which do not correspond to 

 tliose followed by the stones and blocks in the upper boulder- 

 clay." 



A persistent current, however, carrying icebergs, laden with 

 detritus in an already turbid sea, would have the inevitable result of 

 preventing any tender marine organisms, such as mollusca, from 

 settling down in its track, and to this fact, I think, is due the absence 



1 



