Mr Hugh Miller on Boulder-Glaciation. 187 



and develop fluxion-structure, was quite to be expected. It 

 need scarcely be remarked that the other structure to which 

 I have devoted this paper is, generally speaking, a result of 

 the same process. The fluxion-structure is the result of 

 movement ; the pavement-boulders are those elements in the 

 materials that, making of themselves inclined slides, could 

 best resist the movement, and were striated atop in resisting. 

 It does not follow, however, that wherever we find an 

 orientation of boulders in the till there was fluid al motion 

 in the layer in which they lie. If the ice had a fluxion- 

 structure of its own, such boulders as were incorporated within 

 its mass would arrange their axes conformably ; and when 

 they lagged and came to rest and were imbedded, they might 

 retain in many cases the arrangement that marked them when 

 in motion. There seems to be some proof that this was often 

 the case. In many boulder-clays there occurs a certain 

 structure of irregular horizontal planes having some tendency 

 — sometimes a very marked one — to coincide with the sur- 

 faces of pavement-boulders, and dodging unevenly among the 

 others. Some of these wavy planes may be due to pressure 

 — an incipient sort of cleavage developed under the weight of 

 the ice. Sometimes, however, the planes may be seen to open 

 out a little and to include siftings of clay or washes of sand 

 and stones of a different texture to the till; and I believe 

 that they probably are more often due to packing than to 

 pressure. They somewhat resemble these uneven planes that 

 in a packing-case mark the order in which the bunches of 

 straw were bundled in and packed down and smoothed over, 

 and the glaciated boulders and the slight surface washes mark 

 the intervals. Mr Mackintosh, indeed, refers them to aqueous 

 lamination entirely ; but this view does not stand the search- 

 ing examination to which it has been subjected by Professor 

 James Geikie.^ Professor Geikie himself regards them as 

 pressure-planes. I am convinced, however, that in many 

 cases they indicate a rude stratification of that clumsy kind 

 that marks periodical accumulations in which the sifting 

 agency of water has not been concerned, such as the refuse 



^ The Intercrossing of Erratics in Glacial Deposits (Scottish Naturalist, 

 vol. vi., pp. 193, 241). 



