J. G. Goodchild — On the Origin of Counts. 495 



its normal direction ; in the other, local circumstances, which in 

 many cases may have remained constant throughout the whole period 

 of the Ice-sheet, caused the ice to move in a direction more decidedly 

 curvilinear, so that in the end the rock surface was ground into its 

 present form. 



If it be conceded that force can be transmitted considerable distances 

 in any direction through ice, the analogy of a glacier with a river is 

 complete in nearly every respect. We may, therefore, venture to specu- 

 late upon the existence in the great ice-sheet of phenomena parallel 

 to any that are known to occur in rivers. If we examine a shallow 

 river about the point where it is joined by a tributary of considerable 

 size, we usually find that the shingle on the bank of the larger stream 

 opposite the point where it is joined by its affluent is swept away by 

 the conjoined currents, so as to leave a kind of bay with a regularly 

 curved outline, which varies in form and position with the relative 

 directions and intensities of the two currents to whose joint action 

 the deflection of the stream is due. Compare this with what occurs 

 on a larger scale in rock masses : where the larger ice-filled vallej^s 

 were joined by powerful tributaries, the bank opposite the point 

 of junction is ground into a bay of exactly the same form as that 

 swept out of the shingle by rivers of the same relative volumes under 

 like circumstances. The stone-shod ice of the main stream was 

 impelled by that of the tributary against the bank opposite the point 

 of confluence, and the combined effect of the two currents caused the 

 ice to move in a more or less curvilinear direction, until it gradually 

 merged into the direction of the main valley, a long way farther 

 down the stream. The Bolton Castle Coum is an excellent instance 

 of this kind. The ice of the main valley, throughout perhaps the 

 greater part of the ice-sheet period, was kept pressed against its north 

 bank by the two powerful tributaries that came down Walclendale 

 and Bishopsdale, whereby the conjoined streaais were compelled to 

 move slowly in a curve until they flowed again into the normal 

 direction farther down Wensleydale. As the conditions that gave 

 rise to the curvilinear motion remained constant throughout the 

 whole of the glacial period, while the ice maintained not less than a 

 certain thickness, it is quite possible that the result may be due, in 

 this case, as in many others, to the long-continued action of com- 

 paratively feebly acting causes bringing about results that seem at 

 first sight to require more energetic action than that which it is here 

 supposed gave them their present form. 



If we take the case of a powerful stream that is joined by a much 

 smaller affluent — so small that its current produces no appreciable 

 effect upon that of the main stream — it will be noticed that it very 

 often happens at the point of junction that a kind of tangential action 

 is set up by the two forces, so that part of the smaller stream is ponded 

 back into its own channel and is compelled to move in a complete 

 circle — backwards towards the head of the tributary, then round 

 against the upper bank at the point of junction," and finally round 

 into the direction of the main stream — before it can escape from its 

 own channel. As a consequence, the shingle is often swept away 



