CnAP. XIX.] TEIE SURFACE OF THE EARTH. 209 



sand-ridge, every shifting shingle bank formed along- 

 shore by wave or tidal action. It is also that of 

 sand -ridges on a plain, drifted by wind alone, and it 

 is the form of snow-drifts — the point of the wedge 

 being towards the source of action. Whether water, 

 or wind, or both, acting continuously^ have been 

 agents in these conformations ; whether, in contract- 

 ing or expanding, the earth's surface or crust has had 

 a tendency to scale-like fracturing, must be left to 

 the consideration of competent judges.' 



These conformations, observed by Admiral Fitz- 

 roy, appear clearly to coincide with such as might 

 naturally be expected to result from the alternate 

 conjunction and opposition of the two actions of vis- 

 inertia3 in combination with the undulating tendency 

 of lateral pressure. 



Besides the motions of axial rotation and orbital 

 revolution, whose effects we have just considered, let 

 us suppose the earth to have an onward motion 

 southwards, since the evidence deduced from the 

 course of the currents of the ocean has indicated a 

 motion of the earth m the direction of the South 

 Pole or thereabouts. 



And since, according to the theory just sketched, 

 the motion of the earth results from attraction, it 

 seems natural to expect that the movements of the 

 magnetic-needle may be an effect of the action of the 

 force which is carrying the earth onwards in that 

 course. And, if so, we may then infer that the 



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