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Differential Movements of the Ice on various platforms. — Reference 

 has already been made to the differential flow of the ice sheets. 

 Sir Andrew Ramsay, many years ago, expressed an opinion to the 

 effect that it was far from unlikely that the higher parts of a thick 

 sheet of flowing ice might be slowly moving in a direction different 

 from the course taken by the same stream of ice at lower levels. 

 He thought it possible that, under particular conditions, two cur- 

 rents might move even in diametrically-opposite directions over the 

 same point. This idea was, of course, based upon what is known 

 to be taking place on a small scale even amongst the glaciers of 

 the Alps, whose laws of motion are, in other respects, strictly 

 comparable to those of a river placed under like circumstances. 

 In the vestiges of former ice action in the north of England it 

 seems abundantly evident that such must have been the case there 

 also, and that too, to a greater extent than Sir Andrew, at the time 

 he made the observation, seems to have anticipated. The directions 

 of continuous striation seen on many of the glaciated rock surfaces 

 in the North of England shew in the most unmistakeable manner 

 that this must have been the case, on the large scale, as well as on 

 the small. A stream of water flowing over a boulder in its course 

 illustrates this point well. A foot or so above the obstacle the 

 water will be seen to be flowing in ordinary course in the main 

 direction of the stream, while on the level of the boulder itself 

 the stream can be seen to part to the right and the left and to flow 

 for a short distance in courses even at right angles to the main 

 current above. Occasionally, and for a short distance, the two 

 sets of currents may even flow in diametrically opposite directions. 

 The same thing happens, as Mr. James Geikie has pointed out, 

 with a wave breaking on a beach, and the resulting undertow. The 

 courses of glacial strias clearly show that the same phenomena 

 must have been of common occurrence during the Glacial Period. 

 And it is quite clear that the phenomena were by no means limited 

 to the small scale, but, on the contrary, they can be traced from 

 cases covering areas of only a few inches up to areas whose 

 superfices must be measured by miles. This fact has a most 

 important bearing upon the perplexing distribution of certain 



