Ch. SH.] GLACIATION OF SCANDINAVIA. 149 



Scotland, Scandinavia, and other countries, the till and boulders are 

 so connected in mineral and lithological character with the structure 

 of the hills and valleys belonging to the hydrographical basins over 

 which they are strown, that they must have been produced by land- 

 glaciers, although in the same regions drift of submarine origin is 

 occasionally met with. 



CHAPTER XII. 



POST-PLIOCENE PERIOD, CONTINUED. GLACIAL EPOCH, CONCLUDED. 



Glaciation of Scandinavia and Russia — Glaciation of Scotland — Marine shells in 

 Scotch glacial drift — Their Arctic character — Rarity of organic remains in 

 glacial deposits — Contorted strata in drift — Glaciation of "Wales, England, and 

 Ireland — Marine shells of Moel Tryfaen — Norfolk drift — Glacial formations of 

 North America — How far of submarine origin — Many species of testacea and 

 quadrupeds survived the glacial cold — Connection of the predominance of lakes 

 with glacial action — Morainic lakes — Objections to the hypothesis of the erosion 

 of large lake-basins by ice — Conversion of valleys of denudation into lakes by 

 upward and downward movements — Action of ice in preventing the silting-up 

 of lake-basins — How the bed of a sea where icebergs have abounded may, on 

 emergence, afford lake-basins — General causes of change of climate — Submer- 

 gence of the Sahara in the Post-pliocene period a cause of Alpine cold — Meteor- 

 ites in drift. 



Having in the last chapter described the permanent effects which 

 continental ice, glaciers, and icebergs imprint on the surface, I shall 

 now proceed to describe some of the geological monuments of ice- 

 action of more ancient date, or of the Post-pliocene period, observ- 

 ble in Europe and North America. 



Glaciation of Scandinavia and Russia, — In. large tracts of Norway 

 and Sweden, where there have been no glaciers in historical times, 

 the signs of ice-action have been traced as high as 6000 feet above 

 the level of the sea. These signs consist chiefly of polished and fur- 

 rowed rock surfaces, of moraines and erratic blocks. The direction 

 of the erratics, like that of the furrows, has usually been conformable 

 to the course of the principal valleys ; but the lines of both some- 

 times radiate outward in all directions from the highest land, in a 

 manner which is only explicable by the hypothesis of a general 

 envelope of continental ice, like that of Greenland, noticed in the last 

 chapter. Some of the far-transported blocks have been carried from 

 the central parts of Scandinavia toward the Polar regions; others 

 southward to Denmark; some south westward, to the coast of Nor- 

 folk in England ; others southeastward, to Germany, Poland, and 

 Russia, and to these same countries small stones and finer matter 



