180 



Proceedings of the Royal Physical Society. 



Now, all this is unmistakable fluxion-structure. " In what 

 is termed fluxion- structure," says Mr Arch. Geikie, " crystals 

 or crystallites are arranged in current-like lines, with their 



Fig. 10. 



Fluxion-structure around a boulder in vertical section (scale \ natural size), 

 South Tyne, near Haltwliistle. 



long axes in the direction of these lines. Where a large 

 alder crystal occurs, a train of minuter individuals is found 

 to sweep round it, and to reunite on the further side. . . . 

 So thoroughly is this motion characteristic of a somewhat 

 viscid fluid, that there cannot be any doubt that such was the 

 condition of these masses before their consolidation." ^ 



There can be as little doubt that the structures I have 

 described indicate the dragging along of a surface layer of 

 the boulder-clay, accompanied with a shearing movement 

 of particle upon particle, producing intimate glaciation 

 within the mass. 



The Movement Differential. — Thickness of Fluxion- Layer. 



It is not probable that this shearing layer of boulder-clay 

 was thick. A granular movement of the matrix of a kind 

 sufficient to produce striation of quartz grains must have 

 been accompanied with vast friction. Any force, however 

 great, may well have been reduced to nothing when distri- 

 buted among such numbers of inert particles — as the force of 

 a cannon ball is spent when it buries itself in sand. 



The fractured boulder in Fig. 11 seems to indicate in an 

 interesting manner that the movement was difl'erential in 

 character, and, like the movement in a glacier, decreased 



1 Text Book of Geology, 1st ed., p. 104. 



