J. Q. Goodchild—On Drift. 503 



Professor Earn say long since stated it as his belief that there were 

 not only crossing currents in the ice-sheet, but that it was quite 

 possible that some of the higher parts of it may have moved in 

 directions directly opposite to the course taken by those at a lower 

 level. 



Many phenomena, otherwise inexplicable, may be easily enough 

 accounted for by this theory ; such, for instance, as the transportal of 

 drift in directions opposite to the movements of the sole of the ice as 

 indicated by the scratches. 



One remarkable instance of this kind has lately come under the 

 writer's notice, in which the general direction of transportal of part 

 of the drift was clearly up the valley, the far transported drift being 

 intimately mixed up with detritus of purely local origin, and the 

 whole deposit left in considferable masses in the bottom of the higher 

 end of the valley. Yet a small rock exposure in the stream, about 

 two miles from the head of the valley, exhibited a well-striated rock 

 surface, the appearance of which clearly showed that the ice which 

 formed the strias must have moved down the valley. The presence 

 of the drift of extraneous origin, with undisturbed lines of bedding, 

 above the glaciated surface, precludes us from referring these strias to 

 any after glaciation, which must inevitably have swept out all traces 

 of the older drift. 



We are, therefore, led to conclude that in this case, as in probably 

 many others, the bottom ice, acting more under the influence of 

 downward pressure than the higher parts, moved downwards and 

 outwards to the point where its outward motion would be stopped by 

 the up-flowing ice, whilst the higher strata, being more afiected by 

 the local set of the ice currents at the surface, which were acting 

 horizontally, and being less influenced by the overburden of ice, 

 would move towards the head of the valley up to the point where 

 the local ice would check or alter its course. In this case, therefore, 

 it is easy to see how the two currents, over any given spot, may be 

 moving in precisely opposite directions at the same time. 



An exact parallel maybe found in the undertow flowing seawards 

 from a beach, while a little higher up the breaker is advancing 

 towards the shore. 



In cases similar to that of the ice currents just referred to, a little 

 consideration will convince one that there must have been some- 

 where a point at the bottom of the ice at which the two opposing 

 forces, the outflowing and the inflowing, must have been exactly 

 equal in energy, and in which, therefore, the line of least resistance 

 must have lain in an upward direction. This course, therefore, the 

 ice would take ; and many, if not all, of the stones set in the bottom 

 of the ice would go up with it. In proportion as the stones rose in 

 the body of the ice, they would be brought more within the in- 

 fluence of the higher currents, and would in that way be occasion- 

 ally carried backwards in the ice over the spot at which they first 

 worked into it at a lower level. The crossing current, before 

 referred to, would tend to bring about a similar result. Many 

 stones which were fixed in the sole of the crossing streams would, 



