Mr Hugh Miller on Boulder-Glaciation. 185 



dence. Many stones have veered to this side or to that, or 

 tilted into the various positions that give the appearance of 

 structurelessness to the whole; but these variations often 

 cancel one another in favour of the mid-line along which the 

 best index-boulders lay their axes. 



To account, however, for all the variations apparent in any 

 one section, it would be necessary first to see all round it. 

 In the shore-sections near Portobello, there seemed in places 

 to be interferences with the normal direction of fluxion-struc- 

 ture which there was nothing apparent to account for. Behind 

 some large boulders also I seemed to detect considerable 

 confusion. In the tails of drift, whether behind boulders or 

 bosses, confusion might be expected. And in such stiff and 

 slow-moving materials it is difficult to say how long it need 

 take the stones to regain their normal drift} 



III. — Conclusion. 



It would probably be vain to take any one structure in the 

 till and expect it to be universally characteristic. Fluxion- 

 structure, as we have seen, is not universally characteristic, 

 for there are materials too coarse or too raw to assume it. 

 Neither can the surface-glaciation of boulders in their place 

 in the clay be declared to be universally characteristic. There 

 are boulder- clays whose boulders were too small to withstand 

 it. 



^ I have seen no evidence of any regulated eddy. In some cases I have 

 noticed that the force brought to bear upon the front of a boulder had evi- 

 dently compressed the till behind it, imparting a kind of concentricity to the 

 axes of the little boulders. 



There is a peculiarity of structure in the Fillyside till to which I may refer. 

 It was observed by Mr Peach in the hand specimens I showed him, that the 

 small boulders were mostly laid up on edge, as if running on their keels. 

 Now, it might be expected that where there was much lateral pressure the 

 clay might assume some of the characteristics of the cleavage of slaty rocks or 

 of laterally compressed ice. And one of the symptoms of the lateral pressure 

 might be that the little flat boulders would erect themselves on edge. The 

 difiiculty is that, so far as can be seen, there is no compressing cause on the 

 gentle side-slope of an open valley. There is nothing to produce even cleavage- 

 structure in ice. This edge-position of the boulders is not the usual one. I 

 fail to find it in valleys, where it might be much more expected, if this 

 explanation were the correct one. 



