ACTION" OF CURRENTS ON DRIFT. 



253 



clay of Toronto, or the drift on the South Branch of 

 the Saskatchewan, neither is it in the least degree prob- 

 able that the current which could transport such heavy 

 materials would admit of a mixture of clay, sand, shale, 

 and boulders. The materials would be sorted by the 

 current and deposited in the order of their specific gravity. 

 The sorting of materials is one of the most positive proofs 

 of the action of currents ; and where no trace of sorting 

 can be discovered, when fine sand, coarse sand, pebbles, 

 and boulders are present, we may reasonably infer that 

 no current assisted in distributing them. 



Among the foreign materials entering into the com- 

 position of the blue clay, we find granitic masses which 

 have been brought from the outskirts of the fossiliferous 

 rocks in Canada, a distance of at least 100 miles from 

 their present position, and throughout the blue clay we 

 discover also the magnetic oxide of iron. 



The materials of local origin exist in great abundance 

 in the form of fragments and masses of shale, limestone, 

 and clay derived from the underlying shales, &c. The 

 nature of the agent which transported the foreign ma- 

 terials from so great a distance is almost universally ac- 

 knowledged to have been water and floating ice. The 

 finer materials may have been conveyed by water, the 

 coarser drift and erratics would require floating or moving 

 ice. There can be little doubt that both water and float- 

 ing ice (icebergs and floes) have been instrumental in 

 bearing from northern fossiliferous and unfossiliferous 

 rocks a considerable proportion of the numberless erratics 

 strewn over the surface of a large part of this continent, 

 as well as much of the clayey deposits so plentifully dis- 

 tributed north of the 40th parallel. But the symmetrical 

 arrangement of some of the slabs, pebbles, and boulders 



