§10. 



ERRATIC BOULDERS. 211 



existing geographical distribution of the land and water, 

 but must have been effected when the present dry land was 

 beneath the sea, and subaqueous currents and icebergs were 

 in active operation. By the former, the accumulations of 

 sand, mud, and gravel may have been deposited ; and by 

 the latter, the blocks, however large, may have been de- 

 tached and transported from their parent rocks to the distant 

 regions they now occupy.* The general course of the drift 

 and erratic boulders in the northern parts of Europe and 

 America, appears to have been from the north and north- 

 west towards the south-east ; as if the materials had been 

 brought by polar currents from the northern to the southern 

 regions ; hence the term " northern drift " is often em- 

 ployed to designate the alluvium and boulders which belong 

 to this category. 



Over vast regions of the north of Europe, in Poland, 

 Russia, &c. erratic boulders, chiefly of crystalline and palae- 

 ozoic rocks, are profusely scattered over the beds of alluvial 

 debris, and upon the exposed surfaces of the older strata. 

 In Sweden, these phenomena are strikingly displayed. The 

 transported blocks occur in clusters, on mounds and ridges 

 of sandy loam termed osar, sometimes at a height of from 

 200 to 300 feet above the adjacent plains. The origin of 

 these widely spread erratic boulders is the granitic and 

 palaeozoic rocks of Scandinavia. The recent travels and 

 investigations of Sir R. Murchison have afforded a satisfac- 

 tory solution of this problem. It appears that at a very 

 remote period, the granitic rocks of Scandinavia were up- 

 heaved, and their pinnacles split and shattered to pieces, by 

 the expansive effect of ice ; and the fragments and detritus 

 that were carried into the sea by the action of glaciers and 



* The power of icebergs in transporting blocks and immense quan- 

 tities of earthy materials, is graphically elucidated in Mr. Lyell's 

 Principles of Geology, and Sir R. Murchison' s Silurian System; see 

 also several memoirs in the American Journal of Science. 

 p 2 



