GLACIO-AQUEOUS ACTION IN NORTH AMERICA. 219 



rents southerly ; and these, meeting with the easterly currents, the 

 result would be a current compounded of the two forces ; that is, 

 a southeasterly one, — the very direction that seems to have been 

 generally taken by drift over the whole northern hemisphere. 



We might perhaps proceed a step further, and say, that in the 

 effects of present or past agencies, we can recognize the conditions 

 essential to all the preceding theories. In the floating icebergs of 

 the northern and southern hemispheres, we have an example of 

 the transportation of bowlders and smaller detritus from high 

 latitudes towards the equator. In the glaciers of the Alps and 

 other mountains, we can see the precise manner in which the 

 striation, smoothing, and rounding of the rocks, and the accumu- 

 lation of gravel and sand in ridges and tumuli, may have taken 

 place. And in the recent elevation of the Alps and the dispersion 

 of drift from the axis of the mountain, as well as from some of 

 the mountains of Great Britain, and perhaps of Northern Conti- 

 nental Europe, we see the effects of the elevation of large masses 

 of land from the ocean. Is it not therefore possible, that the phe- 

 nomena of drift may have resulted from all the causes advanced 

 in the theories under consideration ; and that the ultimate and true 

 theory on the subject may be compounded of them all? 



But whichever of the preceding views shall prove ti'ue, I feel 

 as if we might now safely take our stand on this conclusion, that 

 the proximate cause of the phenomena of drift has at last been de- 

 termined, namely, the joint action of water and ice. The dynamics 

 of this most difficult subject seem at length to be settled. And 

 now suppose we cannot go back, and determine certainly the 

 origin and mode of operation of these agencies. This will not 

 make it any the less certain that they have existed and have ope- 

 rated. And perhaps geologists will be obliged to content them- 

 selves with this conclusion, however gi-atifying it might be to 

 curiosity, to trace from the beginning, the modus operandi. What 

 if they should never be able to satisfy themselves which of the 

 varieties of theory above described is the true one ? Yet have 

 they reached an immense conclusion, when they have shown, as 

 they seem now to have shown, that the surface on which we 

 dwell, that a large part of the northern hemisphere, and probably 



