On Drift. 9 



of adopting that which would attribute these currents to waves of 

 elevation, resulting from frequent, sudden, but not extensive ver- 

 tical movements of the central range of elevated land ; movements 

 which we may conceive to have been thus repeated while the mean 

 movement of the whole region was one either of gradual depres- 

 sion or of elevation. 



And here I would make an observation which may not perhaps 

 be without its theoretical value. Adopting this view of the sub- 

 ject, we may conceive the centres of the elevatory movements to 

 have been different at different times, and consequently the direc- 

 tions of the corresponding currents produced by them to have 

 been different, as in fact they would appear to have been from the 

 different directions in which the transported matter has been 

 driven from the same original site. But the movements which 

 would send forth the greatest quantity of floating ice would be 

 those which more immediately affected the line of coast ; and the 

 coast being deeply indented, as it must have been, by the present 

 river- valleys when submerged, torrents would be simultaneously 

 discharged from their mouths which would determine, in a mate- 

 rial degree, the resulting current in the open sea ; and since these 

 valley- currents would necessarily have always the same directions, 

 they would tend to impress approximately the same constant 

 direction on the resulting ocean-current, ; whatever might be the 

 precise centre of the elevatory movement. This influence, however, 

 would, of course, be principally felt at points least remote from 

 the then existing coasts. 



When we pass to the great field of northern drift which the 

 continent of North America presents to us, it is not perhaps 

 without some feeling of disappointment that we find the directions 

 of the striae and those of transport without any distinct character 

 of divergency either from local centres or from a general one. 

 The observations described in Dr Bigsby's paper on the " Erratics 

 of Canada," were made before the importance of striated and 

 polished rocks had been recognised, or we should doubtless have 

 obtained much valuable information respecting them from so care- 

 ful an observer. We learn, however, from the American geo- 

 logists, that the strise preserve an approximate parallelism in a 

 north-westerly and south-easterly direction over the north-eastern 

 part of the North American continent, and that the erratic, blocks 

 and other transported matter have come in the same direction. 

 In northern Europe, when the striating agents had quitted the 

 Scandinavian mountains, they met with no other mountains of 

 sufficient magnitude to impede their general course, or materially 

 modify the directions of movement ; but in America the striation, 

 according to the American geologists, has been carried not only 

 transversely but obliquely over some of their highest mountains, 

 without material deviation from its normal direction, except along 



