200 T/ie Scottish Naturalist. 



conclusions arrived at by the Saxon geologists. But, apparently 

 in direct contradiction of this conclusion, we have evidence to 

 show that boulders of the same kinds of rock occur in Denmark 

 and Holland, pointing to a former ice-flow from north-east to 

 south-west and west. Thus boulders derived from Gothland 

 occur at Groningen in Holland, while fragments from the island 

 of Oland are met with in Faxo ; and erratics from the borders 

 of the Gulf of Finland are encountered at Hamburg. Indeed, 

 when geologists come to examine the erratics in North Germany 

 and Poland generally, they find evidence of apparently two ice- 

 flows — one of which went south-south-west, south, and south-east 

 — spreading out, as it were, in a fan-shape towards the southern 

 limits reached by the great " Northern Drift," — while the other 

 seems to have followed the course of the Baltic depression, over- 

 flowing the low grounds of Northern Prussia, Holland, &c., in a 

 south-west and west direction. Now, it is quite evident that no 

 one mer de glace could have followed these various directions 

 at one and the same time. The explanation of the apparent 

 anomaly, however, is not far to seek. It is reasonable to infer, 

 that long before the mer de glace had attained its maximum 

 dimensions, when as yet it was confined to the basin of the 

 Baltic and was only able to overflow the northern regions of 

 Prussia, &c, its course would be determined by the contour of 

 the pavement upon which it advanced. It would, therefore, be 

 compelled to follow the Baltic depression, and for a long time 

 it would carry erratics from Finland, the Baltic Islands, and 

 Eastern Sweden, in a south-west and west-south-west direction. 

 And this would continue to be the direction even after a con- 

 siderable portion of the low grounds of Prussia, &c, had been 

 overflowed. But when the ice- sheet was enabled to advance 

 south into Saxony, Poland, and Lithuania, erratics from Fin- 

 land, the Baltic Islands, &c. would necessarily cease to travel 

 towards the west, and hold on a S. S.E., S., and S.S.W. 

 course. Again, when the mer dc glace was on the decline, 

 a time would return when the ice, as before, would be con- 

 trolled in its flow by the Baltic depression, and this would 

 give rise to a further distribution of erratics in a prevalent west- 

 by-south direction. 1 



1 For a fuller discussion upon the distribution of erratics on the Continent, 

 I may refer to Appendix, Note B, in ' Prehistoric Europe,' where the reader 

 will find references to the literature of this interesting subject. 



(To be continued.) 



